We all have one main antivirus/antimalware software  installed on our computers. (Or do we?) If you have followed dotTech’s advice and have one of the top-notch ones such as avast! , you are fairly well protected. Even with the protection we have (always use protection) there comes a time when one downloads a shady file from a shady website and we are unsure about its safeness; and thus would like to consult more than one antivirus program and get “second opinions”. That is where online multi-engine antivirus/antimalware scanners come in.
^ Image Credit: Daquella manera 
In this article you will find a list of seven free online multi-engine antivirus/antimalware scanners. They are in no particular order, although as you will read below, I clearly have my favorite(s). You are free, however, to use the one you find the most attractive — you don’t have to do everything I say.
Free online multi-engine antivirus/antimalware scanners
I am sure many – if not all – of you have heard the name VirusTotal before. This is because VirusTotal is probably the most popular online multi-engine antivirus/antimalware scanner. I don’t know if it has been around the longest or not, but it is definitely the best in the sense that it uses the most engines (40+) to scan files. On top of that, recently VirusTotal added a “link scanning” service so if you feed a download link into VirusTotal, you will get reports about the download and reports about the reputation of the website the download is hosted at.
VirusTotal is accessible directly via its website; you go there, upload a file or submit a direct download link to a file (20 MB size limit for both), and let VirusTotal do its thing. (You have the option to upload files securely over SSL, if you wish.) VirusTotal keeps hashes of previously scanned files, so if you upload a file that has already been scanned by VirusTotal in past, you have the option to either rescan the file or just view the old report.
If you use Firefox, you can use VTzilla , an official plugin that allows users to easily scan files via VirusTotal without having to download them first. Chrome and Internet Explorer have similar plugins with the name of VTchrominzier  and VTExplorer .
Jotti’s Malware Scan
Jotti is another popular multi-engine online scanner. It uses 20 different antivirus/antimalware engines to scan files. Like VirusTotal, it allows users to upload files directly from its website; however, whereas VirusTotal allows users to submit direct download links, Jotti does not. Jotti also doesn’t have secure uploading. On the bright side, Jotti has a 25 MB file size limit vs VirusTotal’s 20 MB limit.
Jotti does not have any official browser plugin, but there is a program call JottiQ  (unofficial — codded by a DonationCoder developer, not Jotti themselves) that makes it easy to upload and scan multiple files with Jotti.
Novirusthanks Multi-Engine Antivirus Scanner
Novirusthanks Multi-Engine Antivirus Scanner allows users to scan files by uploading them (20 MB size limit) or submitting direct download links (10 MB size limit). It uses 9 antivirus/antimalware scanners. No secure uploading available.
(FYI: I found Novirusthanks Multi-Engine Antivirus Scanner to be very slow when uploading files.)
Metascan Online uses 18 antivirus/antimalware engines to scan files users upload. (No direct download link submission or secure uploading.) The biggest attraction to Metascan Online is it has a size limit of 40 MB: Users can upload files as large as 40 MB.
Oddly enough, when I tested it, I noticed the definitions used by Metascan Online for all 18 of its antivirus/antimalware engines were a week old. I am not sure when Metascan Online updates their engines’ definitions database — it may be on a weekly basis as opposed to daily.
Like all the other websites mentioned above, VirScan scans files users upload; it has a 20 MB file size limit and if a file has been uploaded and scanned before, you are forced to view the old scan as opposed to conducting a new scan. Users cannot submit a direct download link nor is there secure uploading.
In terms of antivirus/antimalware engines, VirScan comes in second place behind VirusTotal with 37 engines.
VirusChief scans files that users upload. (No direct download link submission or secure uploading.) The website mentions no specific limit on file size, but as per my test I was not able to upload and scan a 97 MB file. (Don’t ask me why I picked a 97 MB file — I just did.)
VirusChief claims to scan files with thirteen engines but in reality it appears to only be using six; and to make matters worse, those six engines are very old and out-of-date.
As far as I can tell, VirusChief is a service someone setup in the past and has now ditched. The website and service is still working but the owner is no longer maintaining or updating it. I would suggest avoiding VirusChief unless absolutely necessary because it may give a false sense of security.
Virus.org Scanning Service
I am not sure what is up with Virus.org Scanning Service. I know it used to offer online scanning in the past, but it appears to be down for “maintenance” at the moment. I am not sure if this means it is permanently out of commission or will be back up soon. I just thought I should mention it here in case it does come back up in the future.
Conclusion and Links
Out of all seven mentioned above, the top three in my book are VirusTotal, Jotti, and Metascan Online. Out of these three, my favorite free online multi-engine antivirus/antimalware scanner is VirusTotal. It uses more than 40 up-to-date engines – providing better peace of mind than the others – is fast, and allows users to either upload files (securely or otherwise) or submit download links. Plus the browser plugins make it very convenient to use. Second place comes Jotti, which has a larger file size limit than VirusTotal and has the convenience of JottiQ. Third is Metascan Online for its file size limit of 40 MB — beating out both VirusTotal and Jotti. Care to share which one(s) you prefer, in the comments  below?
You can visit all the websites from the links below:
Metascan Online