I didn't think it would happen to me.

I've found Coinbase to be fine, but if this kind of thing happened to me, well, I used to live with a financial/legal mind of sorts who could probably find all the relevant statutes (he researches these all the time for his job, the ones he doesn't already know--guy is a damn book who reads through like 1100 pages of legal jargon at a time and retains that stuff). I might go talk with this fellow, then find the lawyer he recommends. Financial institutions have a lot of responsibility under the laws and statutes, not to mention common law, and also the duty not to deprive anyone of their property on false premises.

I was also a bit off-put by Coinbase at first, however: initially I did all the steps for instant buy, then made a purchase and didn't get the instant. I also lost out on a lot, though my transactions did eventually go through. Coinbase is not a bad interface or purchasing method if you aren't worried about evading taxes or reporting activity. Bitcoins are lawful, though who knows when someone in an agency may sneakily rewrite either literally or by interpretation some statute to attempt to overreach and attack people to extend their power...if that happens I am, by luck, in with people who could do them hurt (see above) who despite even being slightly statist in some ways, don't appreciate arbitrary power and abuses of government authority and the legal system. Sort-of the old school Bork-types with social liberalism wrapped-up together--see above. (Then there's that I got to know people not far from the current president...I lived across the street from a guy who turns out to work for a Senator and then worked under people who regularly visited with the head of the SEIU just before that person would go see the president...sad that any confidence in not being crapped on comes from those sort of connections--nor would I abuse them to evade legit laws' reach, but we do live in a day of arbitrary abuses so asking people to pull to offset those things isn't a bad way to undermine unlawful governance, even when those people you ask may themselves have their abuses.)

Something odd-ball I'm keeping in mind though: Congress already ruled that "virtual currencies", which at the time were actually in-use for buying things from other people--for real commerce--aren't taxed until a conversion to real currencies: that's the actual rule written by congress...BTC et al isn't even "currency" (mere, note lack of "virtual") since statute deems that to be only fiat (right now, hence people disregarding some of the intentional vaguaries of the FinCen "guidance", i.e. likely mis-guidance: talk to some lawyers who are competent though); it's not even not currency just for that though, because it's a mathematical expression, and it's protocol: if they demanded I surrender BTC I would copy a string and send it to them and say "there you go", because it's just text, and either way (whether sent between wallets/addresses or sending just a numerical copy), copying would be the actual mechanism in play. If and when regulators in the agencies try to pull wait, punish, attack, it's highly likely that not only will they be inadvertently (because typically they can't keep up) shitting on Congressional authority, but then we make sure to highly publicize the fact that an administrative (executive branch) agency is doing so and that should Congress fail to act they could, even in the eyes of the Supreme Court (under some rulings) cede power: the court of public opinion is very useful in that way, as Congress might actually let it happen should it be a benefit, but making all that very public might then backfire, and connecting the dots between that and corruption and arbitrary abuse and carelessness is something none of them need.

And none of that is threat, just something to consider: it's something the political minds I know (including one who has repeatedly been asked to become a speechwriter on both sides of the aisle for all his knowledge in these matters--and after embarrassing as well as getting "politely invited to resign" various people in high positions) talk and think about, and if they're permitted to play loose with "rules" then we can certainly mimic their degrees of twisting and vaguarie and push back.

But one should keep in mind: report the income/gains. That blockchain is not really anonymous, and anyone with half-decent statistical abilities and a slight grasp on a little scripting, can graph the whole damn thing, find every point of entry and contact, and likely work their way back to you. All the software for it exists and, while I'm no programmer, I can conceive of how the mechanisms might work, and even start thinking of how to pseudocode such things successfully enough that a less-inspired programmer could still follow. While I don't buy the dubious rulings that we really need to report income systems, under a truly Constitutional system of governance in the US, we don't have such now, only people at-least slightly-sociopathic who only care what they can get to gain approval and feel effective. I don't even doubt they care little about someone saying that openly. If it is not in their immediate interest, don't expect most of them to bat for your in the arena of justice even if you have a chance, and especially don't feel like the IRS's attached "courts" are going to rule on the law rather than in the IRS' favor (that's the reason a court, by congress, was specially designated--and attached--to the IRS, to specialize in successful collections, their own law be damned: this is that part about often not-caring despite surrendering power by these people, in order to realize some benefit to themselves).

i.e. again, making sure to report these things or, at least to use the special form that say you refuse the source (though that may put you under special examination and trigger and audit, if one is being rational about it) but are reporting all gains. Talk to a lawyer about the congressional unit whether any gains are truly realized before conversion: with the volatility, I doubt it, and frankly it might just annoy the hell out of the IRS agents when each year you have to file an amendment on the bitcoins in question because their value changed so it was really a loss, no really a gain, no really a loss... One thing to always keep in mind about those folks is (1) "it's not really us but Congress that wants your money" (though their collection metrics would reasonably suggest otherwise), and (2) they're bureaucrats, meaning between a rock (the public, that hates them anyways) and a hard place (the politicians uphill who want brown to roll down), so not being an a**hole about it (while making sure to use good lawyers who also neither intentionally make their lives too difficult nor surrender anything upon administrative demand or because of administrative mis-direction/over-reach/claims) is the way to go in that matter.

With BTC et al, it's likely a good idea to retain a lawyer ASAP since what could be twisted to be "gains" for many who use/invest in them are likely major targets for those desperate in the State to cover their asses and find revenue sources since they've over-promised the nation by magnitudes.

p.s. IANAL and the above is not legal advice. For lawyers who would otherwise think otherwise without the disclaimer and try and attack and come after me, please stop being Richards.