Google has a great service for this called Checksum. You upload a file checksum and it validates it against the database of all known bad checksums that might flag your website as unsafe. The pricing is pretty reasonable too and you can proxy file uploads through their service directly.

I'm actually not telling the truth but at what point did you realize that? And what would be the implications if Google actually did release a service like this? It feels a bit like racketeering.