"It turns out that a small number of these bad transactions have been broadcast in the background of the bitcoin network for some time now, but after Mt. Gox went public with its problems, someone cranked up the volume. “Some joker is rewriting thousands of bitcoin transactions and rebroadcasting them,” says Jeff Garzik, a core developer on the bitcoin software. “It’s not a “massive and concerted” attack, probably just a bored teenager with one computer.”"