There is no substitution for a quality antivirus solution, but how many times were you in a situation that you simply have none at your disposal? In such situation, the best you can do is use something that's free and fast. We bring you a list of online virus and malware scanners which will do just fine for a quick scan of the system.
Avast - Online version of popular antivirus software Avast will scan individual files of up to 512kb in size.
BitDefender - An online version of the BitDefender software. Will scan your drives, files, and boot sector. Works only with Internet Explorer.
Computer Associates Malware Scanner - Browse your drives for a file you suspect of being malware and upload it for their scanner to check it for you.
Eset - Just simply click their terms of service and scan your entire system for occurrences of malware.
Freedom - Chck all of your storage inside your browser with this tool based on F-Port.
Jotti's Malware Scan - Uses several scanners at once to scan files that you upload to detect malware that may be hidden.
NanoScan.com - Requires a small download and then accesses a constantly updated database of known threats. Extremely small an fast.
Panda Security - Searches your system for worms, viruses, trojans and more after a small Active X download.
TrendMicro - This service will not only scan for viruses, but also spyware and malware.
VirusTotal.com - Upload a file of up to 10MB in size and let the site run it through over 30 virus engines. If their server is overloaded, they also provide you the option to email the file to them. (via)