Too often, security programs significantly slow down the computer, causing lags in booting up the machine, launching programs and receiving email. Not only that, they can be incredibly annoying, popping up frequent messages or asking questions in techie lingo.

The main screen of the 2009 version of Norton Internet Security is streamlined and even includes a gauge to show much drain the security program is placing on the computer.

Now, Symantec (SYMC) has decided to radically rewrite its main security suite for Windows to directly address these problems. And in my tests, this new product, Norton Internet Security 2009, largely succeeded. It isn’t perfect, but it is the fastest, simplest and least obtrusive security suite I have ever used.

Being quick and quiet is great, but, of course, a security product also has to be effective against the vast number of viruses, spyware programs and other malicious attacks aimed at Windows. I don’t have a security lab in which to test such effectiveness. But PC Magazine does, and the magazine called the new Norton suite’s spyware and virus protection “extremely effective.” The magazine’s tests are described at http://www.pcmag.com/article2/0,2817,2330024,00.asp.

However, I wasn’t impressed with Norton’s optional antispam feature, which caused the only significant problem I ran into in my testing.

The new suite costs $70, and can be purchased at symantec.com and elsewhere. For that price, you get to install it on three PCs and you get a one-year subscription to its updates, which cost $60 thereafter.

Symantec is now including free support, even over the phone, though in my tests this support proved lousy. Norton Internet Security 2009 works only on Windows XP and Windows Vista.

I tested the new security suite on a Dell (DELL) desktop running Vista and on a Macintosh laptop running Windows XP as a “virtual machine,” meaning Windows and Windows programs ran simultaneously with the Mac operating system. Symantec assured me the program would run properly in this latter setup, and I had run the previous version of Norton successfully in the same environment.

The first thing you notice about NIS 2009 is the fast and simple installation. The process took under two minutes on each of my test machines.

File scanning is also much faster, partly because the new suite has a feature called Insight that allows it to skip the scanning and rescanning of many of your files. Insight gathers information about your installed programs and compares them against a list of programs Symantec knows are “trusted,” through either its own research or through scanning results voluntarily submitted by other users. These trusted programs are then exempted from future scans, saving a ton of time.

The new Norton suite has a feature called Insight which calculates how many of your programs it knows are trusted, and therefore needn’t be scanned repeatedly, saving time.

For instance, on my Dell running Vista, an immediate complete scan done before Insight analyzed the computer took more than an hour. But after Insight determined that over 70% of my programs were trusted, complete scans took 10 minutes or less. Of course, your data files, like Word documents and emails, still must be scanned, because they are typically unique.

To minimize the impact on users, the new Norton does scanning and other tasks only when it detects that the computer has been idle for at least 10 minutes. And new virus definitions trickle into your computer invisibly, in the background, rather than all at once in a major process.

Symantec is so certain that its product has a low impact on PC performance that it built a gauge into its new streamlined main screen that shows its drain on the main processor, or CPU.

NIS 2009 is also far less annoying than other suites I’ve used. In normal operation, it notifies you only when it has completed a background task or if there’s a threat or a repair that requires a user action, such as a reboot. And there’s an even quieter optional “silent mode” that can turn off nearly every nonurgent activity of Norton for up to six hours. Silent Mode is automatically activated during full-screen activities, such as playing games or watching movies.

The new suite has a bunch of other features, including a browser toolbar for Internet Explorer and Firefox that warns against fake and malicious Web pages, and that can securely enter your passwords and other information on Web sites. It also has an antispam feature for Microsoft (MSFT) Outlook and Outlook Express.

This antispam feature, which is off by default, was rated as weak by PC Magazine and, in my tests, it caused both Norton and Outlook Express to crash repeatedly in Windows XP running on my Mac. Symantec suspects this is a problem particular to running Windows the way I was on the Mac. After I reinstalled Norton and turned off the feature, all was well again.

But Symantec’s free tech-support service was not only unable to diagnose the problem, it didn’t even know the difference between Outlook and Outlook Express.

Despite this one glitch, I can recommend Norton Internet Security 2009 as a good way to protect your Windows computer with minimal impact on your time and attention.

Find all of Walt Mossberg’s columns and videos online, free, at the All Things Digital Web site, walt.allthingsd.com. Email him at mossberg@wsj.com.

This is especially true if you are the kind of person who saves most of his or her email. That mound of messages can be a treasure trove of contact information and a history of your interactions with hundreds, or thousands, of personal and business acquaintances. It can tell you the phone numbers and job titles of people, and even who you and your correspondents most often copy on email. It’s a sort of social network all its own.

The trouble is, it’s hard to tease all that information out of the typical email program. And that goes double for the most popular, but most bloated and dense, email program of all, Microsoft Outlook (MSFT).

Now, however, there’s a new, free plug-in module for Outlook that adds a set of social-networking and data-mining features right inside the venerable program. This new plug-in for Outlook is called Xobni, which is “inbox” spelled backward and is pronounced “ZOB-nee.” It is completely contained in a colorful vertical panel that lives on the right side of your Outlook screen and doesn’t block or intrude upon Outlook’s own panes or functions.

I’ve been testing Xobni and I like it. The product has some flaws, and is still a work in progress, but I found that it made Outlook much faster and more useful. Xobni turned my Outlook experience from one that was organized by messages and dates into one that was organized by people, relationships and histories.

Xobni, available at Xobni.com, works with the 2003 and 2007 versions of Outlook, whether you are running Windows XP or Windows Vista. The San Francisco start-up behind Xobni, also called Xobni, is working on versions for other email readers, such as Yahoo Mail (YHOO).

Xobni indexes all your stored email, starting with the most recent messages. Once the email is indexed, the Xobni sidebar shows a profile of the sender of any email you have selected in the message list in your inbox or other folders. Each profile is divided into useful sections, and as you drill down into the specifics on each person, the entire sidebar may fill with more detailed information.

At the top of the Xobni panel is a huge search box. This in itself makes it worth installing the program. It is much faster and better than Outlook’s own search, returning results almost instantly and in two lists — people and mail — with the search terms highlighted.

But that’s just the start. Under the search box is the name of the sender of any email you have selected, with a photo, if available, and a bar chart showing how many emails you’ve received from that person and the times of day when that person appears to be most or least active on email. The latter can be a handy guide to deciding the best time to send an email for a quick response.

Under that is a section carrying the person’s phone number, extracted either from Outlook’s contacts or from the person’s email signature or the body of his or her emails. If Xobni can’t find a phone number, you can click on a link that appears where the phone number would have been, to generate an email asking for a number.

Similarly, Xobni can generate an email asking for a meeting with any person in its profile and fill in that email with your open times for the next few days, drawn from your Outlook calendar. You can also open a new, blank email form, preaddressed to the person in the profile, with a single click.

If the person has a profile on the business-oriented LinkedIn social-networking service, the Xobni panel will display his or her job title, employer, and a photo from LinkedIn.

The final three sections in the Xobni sidebar are even more useful. The first one shows the person’s email “network” — a list of everyone that person has placed in the “To” or “Cc” fields of emails you’ve exchanged. The next section is called “Conversations” and displays the entire threads of all the email exchanges you’ve had with the profiled person. Finally, there’s a section listing all the files you have exchanged as attachments with the profiled person.

Each of these sections has its own search, and allows you to open the entries it contains.

There are some bugs. In my tests, Xobni mistakenly merged the profiles of a few people. It also failed to recognize that the emails bearing different versions of a person’s name — like “Thomas” and “Tommy” — but with the same email address, were the same person and should have a single profile. Xobni also can cause glitches during manual syncing of BlackBerrys and other devices. The company says it is working on fixing those bugs.

But, overall, Xobni is a smart addition to Outlook that makes email much more useful.

• Find all of Walt Mossberg’s columns and videos online, free, at the new All Things Digital Web site, http://walt.allthingsd.com. Email him at mossberg@wsj.com.

On Friday, Apple (AAPL) is launching a second-generation iPhone, called the iPhone 3G, which addresses both of those problems, while retaining the look and feel of the first model’s hardware and software.

The base version of the new iPhone costs $199 — half the $399 price of its predecessor; the higher-capacity version is now $299, down from $499. Yet, this new iPhone is much, much faster at fetching data over cellphone networks because it uses a speedy cellular technology called 3G. And it now sports a GPS chip for better location sensing.

The company also is rolling out the second generation of its iPhone operating system, with some nice new features, including wireless synchronization with corporate email, calendars and address books. And there’s a new online store for third-party iPhone programs that Apple hopes will make the device usable for a wider variety of tasks, including gaming and productivity applications. This new software and store will also be available on older iPhones, through a free upgrade.

I’ve been testing the iPhone 3G for a couple of weeks, and have found that it mostly keeps its promises. In particular, I found that doing email and surfing the Internet typically was between three and five times as fast using AT&T’s 3G network as it was with the older AT&T network to which the first iPhone was limited.

Apple’s new iPhone operating system includes an ‘App store,’ where you can browse for, and download, third-party software.

The iPhone 3G is hardly the first phone to run on 3G networks, and it still costs more than some of its competitors. But overall, I found it to be a more capable version of an already excellent device. And now that it’s open to third-party programs, the iPhone has a chance to become a true computing platform with wide versatility.

There are two big hidden costs to the new iPhone’s faster speed and lower price tag. First, in my tests, the iPhone 3G’s battery was drained much more quickly in a typical day of use than the battery on the original iPhone, due to the higher power demands of 3G networks. This is an especially significant problem because, unlike most other smart phones, the iPhone has a sealed battery that can’t be replaced with a spare.

Second, Apple’s exclusive carrier in the U.S., AT&T Inc. (T), has effectively negated the iPhone’s up-front price cut by jacking up its monthly fee for unlimited data use by $10. Over the course of the two-year contract you must sign to get the lower hardware prices, that adds $240, overwhelming the $200 savings on the phone itself. If you want text messaging, the cost rises further. With the first iPhone, 200 text messages a month came free. Now, 200 messages will cost $5 a month, or another $120 over the two-year contract.

The iPhone 3G still has a couple of features that made the first version unpalatable to some potential buyers. It uses a virtual on-screen keyboard instead of a physical one. While I find the virtual keyboard easy and accurate, not everyone does. Also, in the U.S. and in many other countries, the iPhone is still tied to a single exclusive carrier, whose coverage or rate plans may be unacceptable to some.

Here is a rundown of the changes in the new model.

Design: The new iPhone looks almost exactly like the old one. It is the same length and width, has the same big, vivid screen, and has the same number and layout of buttons. The main difference is the back, which is now plastic instead of mostly metal and curved instead of flat. It’s very slightly thicker in the middle, with tapered edges, and weighs a tiny bit less.

The new iPhone 3G (left) delivers much higher Internet download speeds over cellular networks than the original iPhone (right).

Like its predecessor, the iPhone 3G comes in two models distinguished only by storage capacity: 8 gigabytes and 16 gigabytes. The top model is available in black or white.

Apple has greatly improved the audio on the new iPhone. I found the speaker was much louder, for music and for the speakerphone. But the new phone produced an echo when used with the built-in Bluetooth system in my car. Also, the headphone jack is now flush with the case instead of recessed as on the first model, so it can accept any standard stereo earphones.

The camera, however, is still bare-bones. It can’t record video and has a resolution of just two megapixels. The power adapter is now tiny, at least in the U.S., but Apple no longer includes a dock for charging, just a cable.

Software: The basic software is similar. The biggest addition for some users will be full compatibility with Microsoft’s (MSFT) widely used Exchange ActiveSync service, which many corporations use. In my tests, I was able to connect the iPhone 3G to my company’s Exchange servers in a few minutes, and my corporate email, calendar and contacts were replicated on the phone. Any changes I made on the iPhone were reflected almost instantly in Microsoft Outlook on my company PC, and vice versa. Email was pushed to the phone as soon as it was received on the company’s servers.

One drawback: While you can have both personal and Exchange email accounts on the new iPhone, if you synchronize with Exchange calendars and contacts, your personal calendar and contacts are erased.

The new iPhone and upgraded older iPhones also will be able to use a new Apple consumer service, MobileMe, which offers synchronized push email, calendars, photos and contacts.

There are other improvements. You can now delete multiple emails at once, set parental controls and search your contacts. You can also save photos in emails or from Web sites. You can also now open Microsoft PowerPoint files sent as attachments, though I found in my tests that opening larger PowerPoint files crashed the phone.

Some software features missing from the first iPhone are still AWOL on the new one. There’s no copy and paste function, no universal search, no instant messaging and no MMS for sending photos quickly between phones.

Network: Like the old iPhone, the new one can perform Internet tasks using either Wi-Fi wireless networking or the cellphone networks. But the addition of 3G cellular capability makes the new model more useful for Web surfing, email and other data tasks when you’re not in Wi-Fi range. In my tests, in Washington and New York, I got data speeds mostly ranging between 200 and 500 kilobits per second. By comparison, the original iPhone, tested in the same spots at the same time, mostly got cellular data speeds between 70 and 150 kbps on AT&T’s old EDGE network. The new iPhone typically was between three and five times as fast as the old one.

While AT&T now has 3G networks in 280 U.S. cities, and aims to be in 350 by year end, it is converting its cellphone towers gradually, so not all areas of included cities have 3G coverage. The new iPhone falls back to EDGE speeds when 3G isn’t present.

One side benefit to 3G is that in some areas, voice coverage improves. At my neighborhood shopping center, where the first iPhone got little or no AT&T service, the iPhone 3G registered strong coverage. But I still found that calls regularly broke up on some major streets. In New York City, riding in a taxi along the Hudson, one important call was dropped three times on the new iPhone. Finally, I borrowed a cheap Verizon (VZ) phone and got perfect reception.

Battery life: Apple claims that over 3G, the new iPhone can get five hours of talk time, or five hours of Internet use. Talk time is twice as long on the older EDGE network, and Internet time is an hour better with Wi-Fi.

I ran my own battery tests using the phone’s 3G capability. Although I left the Wi-Fi function on, I didn’t connect it to a network, so the phone had to rely on 3G. In my test of voice calling, I got 4 hours and 27 minutes, short of Apple’s maximum claim and nearly three hours less than what I recorded in the same test last year on the original iPhone. In my test of Internet use over 3G, I got 5 hours and 49 minutes, better than Apple’s claim, but far short of the nine hours I got using Wi-Fi in last year’s tests.

More important, in daily use, I found the battery indicator on the new 3G model slipping below 20% by early afternoon or midafternoon on some days, and it entirely ran out of juice on one day. I overcame this problem by learning to use Wi-Fi instead of 3G whenever possible, turning down the screen brightness and even turning off 3G altogether, which the phone permits.

The iPhone 3G’s battery life is comparable to, or better than, that of some other 3G competitors. But they have replaceable batteries. The iPhone doesn’t.

Third-party software: If things go as Apple hopes, third-party software could be the biggest attraction to the new iPhone 3G, and to upgraded older iPhones. By some estimates, there will be hundreds of these programs, some free and some paid, almost immediately.

Apple didn’t supply me with programs for testing, but I managed to try several on older devices upgraded to the new operating system. I tested a game that used the phone’s motion sensors to control the action, and I tested several programs from America Online (TWX), including AOL Instant Messenger; AOL Radio, which streams music from the Internet; and AOL’s Truveo video search engine. All worked very well.

Among the programs Apple has publicly previewed were a sales automation program from Salesforce.com, a game called Super Monkey Ball from Sega and a program for bidding on eBay (EBAY). Also made public were a news reader from the Associated Press, a program for following live games from Major League Baseball and several programs for doctors, including the Epocrates drug reference.

Bottom line: If you’ve been waiting to buy an iPhone until it dropped in price, or ran on faster cell networks, you might want to take the plunge, if you can live with the higher service costs and the weaker battery life. The same goes for those with existing iPhones who love the device but crave faster cellular data speeds. But if you already own an iPhone, and can usually use Wi-Fi for data, you probably should hold off and get the free software upgrade before deciding whether it’s worth getting the new hardware.

Find all of Walt Mossberg’s columns and videos online, free, at the All Things Digital Web site, walt.allthingsd.com. Email him at mossberg@wsj.com.