VirusTotal is the best online virus scanner because in addition to scanning URLs, IP addresses, and files against several different antivirus engines, it can also be used over email or from a desktop to scan running processes. Dozens of different antivirus engines are used to scan files sent to VirusTotal, which means several different perspectives are used to determine whether or not a file is malicious.
* Scans any file type as large as 256 MB
* Input a URL to scan a whole webpage
* Scans IP addresses
* Can upload more than one file using the desktop program
* Share results of a virus scan using a public link
* Works as a browser extension for Firefox, Chrome, and Internet Explorer
* Scans email attachments
* Can be used on Android devices with an app
* Search for past scan results using a file's hash
* Only one file can be scanned at a time using the web interface
* Allowed for personal use only, not commercial
* Email attachment scans have lower priority than using the web interface
VirusTotal inspects items with over 70 antivirus scanners and URL/domain blacklisting services, in addition to a myriad of tools to extract signals from the studied content.
Any user can select a file from their computer using their browser and send it to VirusTotal. VirusTotal offers a number of file submission methods, including the primary public web interface, desktop uploaders, browser extensions and a programmatic API.
VirusTotal is free to end users for non-commercial use. VirusTotal not only tells you whether a given antivirus solution detected a submitted file as malicious, but also displays each engine's detection label (e.g., I-Worm.Allaple.gen).
This is a partial view of a scan I conducted of a downloaded chess engine: