Oct. 6--Last week, Microsoft released a program that addresses this problem. Microsoft Security Essentials is a free download for Windows XP and Vista PCs that provides protection against viruses and spyware without slowing down your system. It also works on Windows 7, which will be released Oct. 22. Security Essentials replaces Windows Live OneCare, a paid program that Microsoft discontinued earlier this year.

As the name implies, Security Essentials supplies the basics: It protects against spyware and viruses. It is not, however, a full-featured suite. For example, it doesn't include a software firewall, which can block intruders or alert you to unauthorized outbound connections. It also does not include a module that specifically scans incoming and outgoing e-mail. But since Windows itself comes with a rudimentary firewall, and Security Essentials will scan any e-mail attachments that get saved to your hard drive, you're covered for most security scenarios.

Microsoft Security Essentials is unassuming from the start. The download at www.microsoft.com/Security_essentials is tiny -- just 8.6 megabytes for the Windows XP version, 4.3 for the 32-bit Vista/Win7 version, and 4.6 for the 64-bit Vista/Win7 version. It also takes up very little memory when running -- on a 32-bit Windows 7 PC, it uses less than 3 MB of memory when idle.

The program installs quickly, but it does check to make sure your copy of Windows is "genuine" -- i.e., not pirated. It also checks for existing antivirus and antispyware programs and advises that you remove them before installing Security Essentials. If you are using Vista or Win7, it disables spyware fighter Windows Defender, which is included with those operating systems.

I've been testing Security Essentials on XP, Vista and Win7 systems. So far, I have yet to detect any impact on performance. In fact, in a discussion on TechBlog, several commentators who also have the software wondered whether it's even working at all!

That's because Security Essentials is quiet and unobtrusive. The only time it alerts you is when it needs upgrading, or its anti-malware definitions need to be updated.

The program's design is simple as well. When you open it, you have only four tabs -- Home, with program status and a Scan Now button; Update, which lets you manually download new definitions; History, which shows recent actions taken; and Settings.

Quick scan is really quick

The Settings screen gives you more control over how Microsoft Security Essentials behaves. For example, you can change how the software reacts when it finds a virus, whether it will scan external drives and flash drives, when automatic scans occur and what files or folders are excluded from scanning.

You can do three types of manual scans: Quick, Full and Custom. Quick scans, which look in the places malware is most apt to hide, are indeed zippy. A quick scan on a 32-bit Win7 system with 12.6 gigabytes of files to check took 55 seconds. On a 64-bit Win7 system, quick-scanning 59 GB took 1 minute 20 seconds. Full scans will take significantly longer, depending on how many files are involved.

Time is the true test

What we can't know about Security Essentials is how effective it is at preventing and removing viruses. It blocked the test viruses I threw at it, but you'd expect it to do that. Time will tell as to whether it keeps users safe in the real world.

Microsoft has said this package isn't meant to compete with the more full-featured offerings from companies such as Symantec and McAfee. But if your security needs are simple, or you're on a budget, it's an excellent choice. It's also a good option for users who are frustrated with how intrusive and slowing the bigger suites can be.

In the past, I've recommended AVG Free (http://free.grisoft.com) for those who want a no-cost security option. Given its light footprint, I think Microsoft Security Essentials is now the better choice.

dwight.silverman@chron.com http://blogs.chron.com/techblog

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