Windows Defender- good or bad?
Solution 1:
Defender is just an anti-spyware kit. It's not going to stop all viruses so you'll still depend on a decent virusscanner. But it can replace some of the McAfee features.
Solution 2:
Windows Defender is old.
Check out Microsoft Security Essentials, which "provides real-time protection for your home PC that guards against viruses, spyware, and other malicious software. ". MSE came out in mid-2009. It's free for licensed Windows installations.
Consumer Reports rated Anti-malware program in their latest issue, and Microsoft Security Essentials is one of the top free contenders. The report is available in the June 2010 issue, article "Security software" (still on the stands now), or via a paid subscription to www.consumerreports.org.
Solution 3:
I've yet to see any use for Windows Defender, in my limited exposure to it, other than to alert me that there wasn't any recent updates on the system. The security control panel is often more talkative than the windows update system.
Personally I've always used Kaspersky Anti virus. They do have an "internet security suite", but considering the additional resources it uses over the "anti virus" option, I go for the AV. It's very fast, updates every 2-4 hours (although you may set this option to anything you'd like), and I've used it time and time again to pull infected windows installs from the dead.
Just a happy user of it, although I'm primarily a Linux user at home, I do support 40+ Windows workstations, and all of them are well protected with Kaspersky.
Solution 4:
Windows Defender is an anti-spyware program, not an antivirus program. You still need a separate antivirus program. Some computer security suites include antispyware programs, and so you may be able to uninstall (on Windows XP) or turn off (on Vista) the Windows Defender functionality if you have this threat covered in another way.
I have McAfee VirusScan on approximately 90 machines, and I know first-hand that it can, indeed, slow your computer down, but you can configure it at a very fine level of granularity. As always, performance and security involve trade-offs. The more things you want VirusScan or any other antivirus program to check, the more processor and memory resources it will use.