There was a pastebin fairly recently that suggested exploiting the fact you can attach short amounts of data to the blockchain by spamming the network with transactions that contain signatures for random viruses. Thus being flagged by tons of AV software, and potentially causing a loss of coins.
Although it can't actually cause loss of coins. It can only cause problems for local clients, and I think the pastebin over-states the effect.
My Win8.1 PC reported a virus detected in the Bitcoin database today. I just marked it as "Allowed" and then told it to ignore the Bitcoin directory there-after. If I'd picked the default action of "Quarantine" instead, I imagine I'd have been able to unquarantine it later, or else just download the block again. As it is, not only am I fine, but I can re-broadcast the block to anyone else who needs it. As long as one person has a copy, we're fine. The crypto means the block can't be forged. No coins are going to be lost.
It's mostly just to fuck with people who are too stupid to configure their antivirus properly.
