Now, this is going to be a completely unfounded conspiracy theory. I am NOT saying it happens, I am NOT saying it happened in the past, I am NOT claiming it will ever happen.
It's just a concept, that may potentially be a problem.
What would happen if banks, governments, or other organizations that do not like Bitcoin, were to pay vendors of antivirus/antispyware software to include a definition that detects and removes Bitcoin wallets? This would be fairly easy to do, and would possibly cause a lot of chaos as wallet files disappear of people who didn't back them up.
Now the obvious counterargument would be... "wouldn't that damage the reputation of that AV vendor and effectively take out the company?"
No, it probably wouldn't. First off it's fairly easy to blame it on a 'false positive', apologize, and just ignore what happened after that. I believe AVG has, twice, removed critical system files in the past as a false positive, thereby bricking entire Windows installations. "Shit happens", and that would be a very believable explanation to the general public.
Second off, does anyone remember the case where Gator/Claria paid/bribed several antispyware vendors to not automatically remove their adware? It's a bit hard to find sources on this, but I remember reading a few articles about it a few years ago. Some indications are here: http://www.dslreports.com/forum/r13552245-Adaware-delisting-Claria-and-WhenU-
An article about Microsoft suggesting Ignore instead of Remove for Claria can be found here: http://www.theregister.co.uk/2005/07/07/ms_downgrades_claria_detection/
There are undoubtedly more news articles on all of this, but I don't have a lot of time to search for them right now.
What if a similar thing happened where organizations would pay AV/AS vendors to remove Bitcoin wallets 'accidentally'?