If we have to check one computer for viruses and we don’t have any antivirus at hand, F-Secure Online Scanner may be a good option, as it allows you to scan your files without installing any software in your computer.
You only have to browse to its page and download an ActiveX control which will scan the computer searching for viruses. You will need to use with Internet Explorer, as this is the only supported browser.
Another service I like to use is VirusTotal, which offers free online analysis of files with 23 different virus scanners, although in this case you can only scan individual files one at a time, but it is very useful in case you are suspicious of a file and want to test it throughfully. As no antivirus is 100% reliable, checking the file with so many different scanners may guarantee better results.
Anyway, it’s always a good solution to have a resident scanner which avoids viruses even being written to your disk, even less getting executed.
It is a very good antivirus program and it is a very reliable software.