[jjeaff]

If you itemize deductions, and the loss is large enough, you can deduct a loss or theft.

So if you mined and then traded $100k in Bitcoin for Ethereum and then the Ethereum was stolen, you would use form 4684 to claim the loss against your taxable income.

But I haven't heard of anyone doing this yet and I can imagine it would get some scrutiny from the IRS, seeing as it would be hard to prove a loss or theft.