From a report at the link below:
A computer botnet is known to have breached almost 75,000 computers in 2,500 organizations around the world, including user accounts of popular social network Web sites, according Internet security firm NetWitness.
The "Kneber botnet," as it's known, gathers login credentials to online financial systems, social networking sites and e-mail systems from infested computers and reports the information back to hackers.
A botnet is an army of infected computers that hackers can control from a central machine.
The MSNBC report says “unfortunately, it gets easier all the time to become a cybercriminal. Online toolkits, often originating in Russia, make it easy for first-time crooks to get into the botnet business.”
Link