It seems MSE does not find the Virus signature in every Software. I got W7, bitcoin core 0.9.1 (newest Version) and when I run MSE no warning appears
Interesting. So we have no confirmation of this story so far. Is it a hoax?
Also, I have not found any information about which block exactly should contain the virus signature.
It's not a danger to the blockchain.
From
http://antivirus.about.com/od/whatisavirus/a/virussignature.htmIn the antivirus world, a signature is an algorithm or hash (a number derived from a string of text) that uniquely identifies a specific virus.
The idea is that the signature is only a part of that particular virus, so any program with that signature can be assumed to be that virus. If the signature is inserted into the blockchain, then MSE assumes it's a virus.