From the about page:
VirusTotal, a subsidiary of Google, is a free online service that analyzes files and URLs enabling the identification of viruses, worms, trojans and other kinds of malicious content detected by antivirus engines and website scanners. At the same time, it may be used as a means to detect false positives, i.e. innocuous resources detected as malicious by one or more scanners.
Nothing will ever detect 100% of the maliciousness out there but at least you can throw about 54 antivirus scanners (at the time of this writing) at a suspicious file.