"In the first six months of 2012, the threat family Win32/Keygen, representing software activation key generators, was detected nearly five million times. Keygen detections have increased by a factor of 26 since the first half of 2010 and today Keygen is the number one consumer threat family worldwide, rising above other prevalent threat families like Pornpop, Blacole, Conficker and FakePAV. The prevalence of Keygen varies from location to location, however it is listed as a top 10 threat for 103 of the 105 countries/regions studied in SIRv13. That means Keygen is in the top 10 list of threats for 98% of the locations we provide analysis for in SIRv13."
Since of course no one here would be familiar with key generators, would have never looked for, let alone used such a thing... ;?P
As you know apps often use license keys -- individuals/teams reverse engineer apps to determine how they check for legitimate keys, & then either figure out a way to bypass that part of the app's code & release a Crack, or come up with a Keygen, an app that generates keys whatever program will consider legitimate. It's a cat & mouse sort of thing, with new versions of targeted apps blocking Cracks & Keygen generated keys, so those using such things are return or repeat customers, perhaps helping make it a great environment for spreading malware.
And lest anyone think everyone using a crack or keygen is bad, or at least terribly naughty, sometimes DRM is so intrusive people who actually own an app or game will use a crack or keygen to get what they feel they paid for, sometimes that's the only way to trial an app [software marketing does lie], & of course some people, especially in developing parts of the world, simply & truly can't afford to buy software.