STUXNET

Year: 2010

Alleged source: Israel

Fallout: Discovered in June 2010, the Stuxnet worm exploits a vulnerability in Windows to attack Siemens industrial systems, such as those used in nuclear power plants. While systems in several countries, including the United States, were affected, Iran was the worst hit, with over 16,000 computers infected. The virus seemed to be specifically targeting Iran's nuclear program, leading to suspicions that it had been designed by Israel. The Israeli government has neither confirmed nor denied involvement, but a 2011 New York Times investigation concluded that the worm had been developed and tested in Israel.

50 DAYS OF LULZ

Year: 2011

Alleged source: LulzSec

Fallout: In the spring and summer of 2011, a group of hackers calling itself LulzSec, associated with the online collective Anonymous, went on a tear, disabling and defacing a series of prominent websites. Unlike previous large-scale cyberattacks, the group didn't seem motivated by profit or a particularly ideology, but were in fact, in it for the lulz. The group did occasionally take a stand. For example, in response to a documentary about WikiLeaks that it thought was negative, it posted a story on PBS's website alleging that Tupac Shakur is alive. The group also took down CIA.gov at one point. In its biggest operation, Lulzsec hacked into Sony PlayStation's website, compromising the personal information of more than a million users. In June, the group announced through its Twitter feed that it was suspending its campaign, releasing a trove of classified AT&T documents as a parting shot. In July 2011, police arrested an 18-year-old man in the Shetland Islands said to be "Topiary," one of the Lulzsec ringleaders.

THE SOUTH KOREAN DDOS

Year: 2011

Alleged source: North Korea

Fallout: DDOS attacks in March 2004 targeted more than 40 South Korean websites, including those of the National Assembly, military headquarters, U.S. forces in South Korea, and several major banks. The attacks shut down the country's stock trading system for several minutes. An estimated 11,000 personal computers may have been infected by malware as part of the attack. A month later, an attack brought down the network of a major South Korean bank. The South has accused North Korea of running an ongoing cyberwarfare campaign since similar smaller attacks in 2009, but no solid link to Pyongyang has been proven.

ANONYMOUS

Years: 2011-2012

Alleged source: A loose coalition of online "hacktivists"

Fallout: The online group known as Anonymous was, until recently, best known for its attacks on the Church of Scientology and Fox News host Bill O'Reilly. But lately it has taken on more of a political character. Anonymous targeted Egyptian government websites during the uprising against Hosni Mubarak, and when the regime took the unprecedented step of shutting the country's Internet down, the group went old school, flooding government offices with faxes. In response to the January arrest of Megaupload founder Kim Dotcom, Anonymous shut down the websites of the U.S. Justice Department and the Recording Industry Association of America, as well as those of several record companies and congressional offices. In February, the group took credit for shutting down the website of the CIA.

INDIA

Year: 2012

Alleged source: India or China

Fallout: This January, U.S. authorities began investigating allegations that Indian intelligence operatives had hacked into the emails of the U.S.-China Economic and Security Review Commission, an American agency that monitors trade policy was China. The investigation came after hackers posted a document online purporting to show Indian military intelligence plans to target the commission as well as extracts from the emails in question. Just a few weeks later, however, the document was found to be fake -- though the emails were real -- and investigators are now focusing on Chinese hackers as the most likely source of the breach.

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