Every day, all over the world, computer networks and hosts are being broken into. The level of sophistication of these attacks varies widely; while it is generally believed that most break-ins succeed due to weak passwords, there are still a large number of intrusions that use more advanced techniques to break in. Less is known about the latter types of break-ins, because by their very nature they are much harder to detect.

An attacker can monitor the processor's performance in a side-channel and discern important details about the data. This information improves the chance, or in some cases guarantees, that subsequent attacks will succeed.