A number of articles appeared recently linking to a leaked document about Bitcoin written by the FBI.
Bitcoin Virtual Currency: Unique Features Present Distinct Challenges for Deterring Illicit Activity
What involvement or interest has the FBI had with other alternative currencies, such as Liberty Reserve, Dwolla, e-gold, etc?
This question should help provide some context to compare with the interest they've shown in Bitcoin.
There was quite a hype in the US about how bad Bitcoin is, and how they were going to crack down on it. I suppose this report comes from those feelings. Liberty Reserve has actually been closed recently, by the police forces.
Their interest is chiefly identifying and, if possible, removing threats. The EU actually has a similar (but better) report, to assert the status of digital alternative currencies.
The red thread to all of these documents is "Bitcoin is independent of law. Bitcoin cannot be legally prosecuted, and if it could it would be difficult to do it. Anonymity makes it suitable for criminals but it isn't fully anonymous, so maybe we can do something (because of the blockchain). Personally we think Bitcoin is pretty cool.". They also somewhere seem to understand there is a legitimate purpose to Bitcoin, but it's unclear whether that matters or not.
It's very hard to look into the mind of a millions of people wide security organization. If we don't know something it probably exist but it's still classified. This document had only public sources, so did not need classified status. They likely have build a much more detailed document now with knowledge from the NSA (about cryptography) and from Bitcoin companies in the US.
The NSA, meanwhile, has likely been tracking Bitcoin usage very closely. It likely has a pretty good way to de-anonymize Bitcoin traffic. All the aforementioned are, of course, as unprovable as PRISM was.
Most police forces in the world will have reports or accumulated knowledge about Bitcoin because it presents "a novel challenge to law enforcement". These reports will contain "nothing we didn't already know" and reflect the legal perspective of the agency, but only the mood the report writer thought his boss wants.
Good luck people. The police are our friends. Sometimes in the "Do not run, we are your friends" kind of way, sometimes as the robot friend.
