Almost all reputed antivirus company now have free online scanning service. You can get your computer completely scanned online for any possible virus, spyware, adware, trojans etc. by these sites online.
Advantages of online scanning are:
- Online scanner database is very updated.
- You can scan by different provider.
- Its free!!
But please note, its little slow compared to scanning by installed security software.
Here is list of top nine free online scanner.