Not just Bitcoin apparently, others like Ethereum, Dash, Monero and Zcash may also be targeted.
Basically they are replacing cryptocurrencies addresses when they are copied, so by the time you paste it a different address would be entered instead.
So far some $100,000 have been stolen, that's about 23 BTC.
Now you know, make sure to double-triple check that address before you click to send. We should be seeing more of these schemes as cryptocurrencies become more popular.