Reverse Hash Calculator

A few months ago, while reading some news, I found this website where you can enter a md5 or sha1 hash and have a good change of 'hitting' the original value. I don't think it affects digital signatures of documents at all but it is definitely something that network/system administrators should be looking at.

Check the photo below that a friend of mine sent me a while ago, it made me laugh a bit:

Regards,
Tulio de Souza