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.

These types of attacks are called “social engineering,” and they are used by criminals to steal your money and identity, and to plant on your computer malicious software that can be used to keep ripping you off. Social engineering is the online equivalent of an old-fashioned con game, in which a crook frightens people with false warnings, or tempts them with false promises, and then robs them.

While viruses and spyware overwhelmingly afflict Microsoft’s (MSFT) Windows users and spare users of Apple’s (AAPL) Macintosh computers, social-engineering schemes can ensnare Mac users as well. There’s nothing inherent in Macs that makes their owners more resistant to falling for social-engineering scams.

The most common form of social engineering is called phishing, a one-two punch using both email and Web browsing to trick people into typing confidential information into Web sites that look like the sites of real companies, especially financial institutions. But these phishing sites are actually skillfully designed fakes that transmit your sensitive data to criminals, often in distant countries. Once these creeps have your passwords and account numbers, they can loot your funds and steal your identity.

Here are some tips to help you avoid being the victim of social engineering, updated from a similar column I wrote in 2006. It includes information on some antiphishing software that wasn’t available back then. But remember: Security software alone can’t save you from scams.

1. Never, ever click on a link embedded in an email that appears to come from a financial institution, even if it’s your own bank or brokerage and even if it looks official right down to the logo. The same goes for payment or auction services, like PayPal or eBay (EBAY). Don’t do this even if the email asserts that your account has a problem, or that the bank has to verify your information. And certainly don’t enter any passwords, Social Security numbers or account numbers directly in an email.

These types of emails are almost always fakes, and the links they contain almost always lead to phony Web sites run by criminals. The only exception might be a confirmation email from a brokerage firm concerning a trade you know you made minutes before. Even legitimate-looking addresses in emails or in the address bar of Web browsers can be fakes that hide the crooks’ true Web addresses. The lock icon on a Web site can also be falsified.

If you are truly worried about your account, call the bank or company, or go to its Web site by manually typing in its address or by using a well-established bookmark in your browser that you created yourself.

2. Don’t click on links to offers for free software or goods that you receive in an email, especially from a sender or company you’ve never heard of.

3. Never download software from unfamiliar Web sites unless you are absolutely sure you need it and it’s legitimate. Even if it claims to be a useful program, it may very well be a malicious application like a “key logger,” which can report back to crooks everything you type into your computer. If you really want the program, do a Web search on it first, to see if others have reported it as a malicious fake.

4. If a Web site tells you that you need to download special viewing software to see its videos, don’t do it. Even if it claims to be giving you legitimate viewing software, like Microsoft’s Silverlight, Adobe’s (ADBE) Flash or Apple’s QuickTime, don’t download it there. Go to the official Microsoft, Adobe or Apple Web sites to get these viewers.

5. Use a Web browser, like Internet Explorer 7 on Windows, or Firefox 2.0 on Windows or Mac, that includes built-in features to warn you about, or block access to, known phishing sites. The next versions of these two browsers will have even stronger features that will detect sites that are not only fake, but which are known to distribute malicious software.

Unfortunately, the third major browser, Apple’s otherwise excellent Safari for Mac and Windows, lacks any such antiphishing detection, though I expect Apple to add the feature in a future version. So, for now, Mac users worried about phishing should rely on Firefox.

6. Consider security software that tries to detect and block phishing sites. McAfee’s (MFE) free Site Advisor and paid Site Advisor Plus products do a good job. Symantec (SYMC) has similar features built into its large security suites, Norton 360 2.0 and Norton Internet Security 2008.

7. Educate yourself by reading about social engineering and phishing and how to avoid being a victim. Microsoft has a very good guide at: microsoft.com/protect/yourself/phishing/identify.mspx and Symantec has one at: symantec.com/norton/clubsymantec/library/article.jsp?aid=cs_phishing.

Follow these tips and you’ll be a happier — and safer — surfer.

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.