Sim
Administrator
I'd recommend putting the money you'd have to spend on a good anti virus / anti malware program for Windows XP is better put towards upgrading to Windows 7 which comes with an excellent MS built one for free. Stuff like this is (almost) a thing of the past since Win 7.
I disagree completely.
I've seen Win7 machines completely borked by viruses and malware.
For example - my sister is a high school teacher - school computer networks are fertile breading grounds for viruses and malware and she made the mistake of taking her laptop to school. After spending several days trying to clean the mess, I ended up needing to rebuild the machine from scratch to get rid of everything completely. I then installed some real AV/AM software.
Unless you are in a very low risk environment, I would never trust my computer to Microsoft's built in AV software.
Look at recent test results comparing all the major AV software products ... Microsoft Security Essentials used to be able to hold its own several years ago, but fails miserably in more recent tests - it just doesn't get updated like the dedicated software products (who live and die by their ability to make good security software!).