If you suspect you're having viruses on your computer but don't want to install programs that will have a process running thereafter, online scanners are quite good. I already mentioned
Eset Online Scanner.
Others I have used:
There are/has been others, but these are still available and working.
For other malware than viruses, the AntiMalware is my #1 these days, but the
SuperAntiSpyware is also good. It has a portable version, which can be run from a memory stick. It also has some special "Repairs" button, which includes many tools to restore settings after some malware has altered them. Also the good old
Spybot-Search and Destroy seems to have caught up again. When installing it, be cautious with the all-time tools it offers. TeaTimer can be a nuisance. And don't forget the very special
ComboFix, which has saved my bacon numerous times when nothing else is allowed to run.
And then, there's the plethora of
live CD's, another listing
here, from Avira, AVG, BitDefender, F-Secure, Kaspersky Labs, Norton, Panda, Trinity (several brands), you name it. Since they're mostly Linux based, each version can't necessarily use your network card for updating. In that case, there might be an alternative updating method or, you can use another brand.
Happy hunting!