Enlarge The world has seen the most unsettling attack yet resulting from the so-called Rowhammer exploit, which flips individual bits in computer memory. It's a technique that's so surgical and controlled that it allows one machine to effectively steal the cryptographic keys of another machine hosted in the same cloud environment. Until now, Rowhammer has been a somewhat clumsy and unpredictable attack tool because it was hard to control exactly where data-corrupting bit flips happened.