Some malware will crash services. I notice Vundo will cause major instability and is not detected by a lot of anti-Malware or AV software.
I personally use Avira Free for AV, actually catches infections unlike avg...
and i use Malware Byte's Anti-Malware to clean up spyware/malware from all machines. Shop tested this is the best anti-malware software i've used. I must tell you though that some anti-malware software do not fully remove infections like that. Files are left behind that may force the malware to re-install itself after removal.
So best practice would be to install avira first, install malware byte's anti-malware (get it from download.com, main page in the numbered list of most popular).
Update malware byte's, do a full system scan. If you have avira installed then during the scan it may go off due to finding some hidden infections that aren't picked up by your AV software initially.
IF YOU SEE Vundo in the detected list you MUST run combofix to finish removing the infection. google combofix (bleepingcomputer's forum will have the download link). I cant tell you honestly how many hundreds of machines that have come through our shop that have been infected with vundo and all had AVG installed...
Cleaning the infection will save you from having to repair the OS (which doesnt really fix it if there is an infection and is a waste of time) be SURE before you run the repair. The only time I've had to repair the Os after cleaning were from malware that destroyed Rundll32 (not allowing you to run anything at all like windows doesnt know what to do with an exe) or damaged some other system service(s).