This year saw a number of sensational instances when the Web sites of various government agencies and corporations were hacked, in what appeared to a series of cyber-wars, initiated by a group of hackers.

This may sound grim but 2011 was, in several ways, the Year of the Hackers, with damages rumored to be running to millions of dollars.

Hacker group Lulz Security (LulzSec) claimed responsibility for a number of large-scale data breaches and, working closely with another hacker collective called Anonymous, LulzSec encouraged other groups and individuals to open fire on any government or agency that crosses their path. They named the undertaking as Operation Anti-Security.

Check out the slideshow for more details on the most sensational hacks of 2011.

Sonys PlayStation Network
Sony's PlayStation Network Reuters
Citigroup Credit Cards
The Securities and Exchange Commission's enforcement officials are reportedly going to recommend that the agency appeal a scathing opinion from a federal judge in Manhattan rejecting a $285 million settlement with Citigroup. Reuters
The FBI and the CIA
The FBI and the CIA Reuters
The U.S. Senate
The U.S. Senate Reuters
Lockheed Martin
Lockheed Martin Reuters
International Monetary Fund
International Monetary Fund Reuters
Sega Corp
Sega Corp Reuters
Gmail Accounts
Gmail Accounts Reuters
The Pentagon
Sequester cuts will force the Pentagon to reduce defense spending by about $45 billion and furlough hundreds of thousands of employees. Reuters
NASA, Booz Allen Hamilton, Arizona Police and Others
NASA, Booz Allen Hamilton, Arizona Police and Others Reuters
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