Online virus scanners don't offer real-time protection and so should never be considered a substitute for an installed antivirus scanner. But if you suspect your installed antivirus is missing a threat or you simply want a second opinion, an online scanner can be a valuable tool to use. True online scanners are rare - today, many require a download and install and most only support Windows. However, if you use a Mac and only have a specific file you want scanned - or a website checked - there are online scanners available. The list below offers a full range of online virus scan options.
VirusTotal lets you submit files online or via email. The file is scanned by several different scan engines and detection results are reported for each. Submitted files can be up to 20Mb and over 30 virus scanners are used during the scan. Files can also be submitted in bulk, up to 20 requests every 5 minutes for the general public with other options available for bulk and private users. VirusTotal also provides a reporting feature that lets you search for previous reports of files others have submitted.
Like VirusTotal, Jotti returns scan results for several different scanners. The scan engines used by Jottie differ from those used by Virustotal and thus it's often worthwhile to use both.
AVG LinkScanner DropZone is an online Web page scanner that lets you copy/paste a link you recevied in email, Twitter, Facebook, etc. and scan the page for malware before you visit it.
ESET Online Scanner uses ActiveX if Internet Explorer is used, but if a different browser is used a download and install is required. Definition files are also downloaded to the computer, rather than managed online. This can cause some conflict with your normal installed antivirus. Windows only.
Trend Micro's Housecall requires a download and install, which almost negates its being a true online scanner. However, the donwload is tiny and detection still takes place online. The download method also removes the reliance on ActiveX and Java, and it allows the scanner to work regardless of which browser you use. By default, Trend Micro Housecall perfroms a quick scan, only searching common locations and only looking for active malware. Windows only.
Microsoft Safety Scanner requires a download and install. The download is only good for 10 days after which a new download must be obtained. Windows only.
The online Kaspersky File Scanner checks single files less than 1Mb in size. Multiple files can be zipped as one and scanned, provided the resulting archive is 1Mb or less. If you only want to check a single file, you're better off using VirusTotal or Jotti which can handle larger file sizes. Windows only.
BitDefender Online Scanner offers online virus scanning through Internet Explorer. Windows only.