Below is a timeline tracing the roots of this increasingly menacing challenge facing nations and businesses all over the world. As the timeline that follows illustrates, China appears to be the biggest aggressor when it comes to cyber attacks. This timeline covers cyberattacks on government and military computers; it does not include attacks on corporations or individuals. However, events are included if they were carried out by foreign governments or militant groups.

December

The Department of Defense establishes the Joint Task Force on Computer Network Defense to defend the department’s networks and systems “from intruders and other attacks.”

February

President George Bush announces the creation of a new office under the Department of Homeland Security, the National CyberSecurity Division, and lays out a National Strategy to Secure Cyberspace to protect the nation’s computer and information systems from a cyberattack.

November

Hackers, believed by U.S. officials to be backed by the Chinese military, search to find vulnerable computers in the military’s computer network and steal sensitive information. The attacks continued for about three years and were given the name Titan Rain by U.S. officials.

June

The email account of U.S. Secretary of Defense Robert Gates is hacked. Officials blame China’s People’s Liberation Army.

September

British government officials announce that hackers have breached the computers of the Foreign Office and other government agencies. The hackers are believed to be members of China’s People’s Liberation Army.

October

Pentagon officials discover that a flash drive containing a covert program was inserted into a laptop at a base in the Middle East. The program collected data from a classified Department of Defense computer network and transferred it to computers overseas. Government officials say the hack was carried out by a foreign intelligence agency and called the intrusion, “most significant breach of US military computers ever.”

March

Canadian researchers at the Munk Center for International Studies at the University of Toronto, announce that hackers based in China had penetrated almost 1,300 computers in 103 countries, including those belonging to embassies, government offices, and the Dalai Lama, and stole documents and other information.

December

News reports say that Iraqi insurgents had hacked into live feeds being sent by U.S. drones to military officials on the ground.

June

Security experts discover Stuxnet, the world’s first military-grade cyber weapon that can destroy pipelines and cause explosions at power plants and factories, as well as manipulate machinery. It is the first worm that corrupts industrial equipment and is also the first worm to include a PCL (programmable logic controller), software designed to hide its existence and progress. In August, security software company Symantec states that 60% of the computers infected with Stuxnet are in Iran.

August

The Pentagon declares cyberspace the “new domain of warfare.”

November

Iranian president Mahmoud Ahmadinejad acknowledges that the Stuxnet worm destroyed about 1,000 of the country’s 6,0000 centrifuges at its nuclear facility in Natanz. Israel and the U.S. are believed to be behind the attack in an attempt to slow Iran’s progress toward obtaining nuclear weapons.

December

Anonymous attacks several businesses seen as “enemies” of WikiLeaks. The action was in response to the arrest of WikiLeaks founder, Julian Assange. In 2010, WikiLeaks provided several news organizations with hundreds of thousands of secret government and military documents about the wars in Iraq and Afghanistan, as well as cables that gave a behind-the-scenes look at American diplomacy from the perspective of high-level officials.

December

Malware, named Mahdi after the Messiah in Islam, infiltrates about 800 computers of government officials, embassy employees, and other businesspeople in Iran, Israel, Afghanistan, the United Arab Emirates, and South Africa. The malware was embedded in email attachments and users who opened the documents were susceptible to having their emails and instant messages read by hackers.

May

The U.S. Department of Homeland Security announces that spear fishers have penetrated the computer systems of U.S. gas pipeline systems.

August

Hackers, who say they are Islamic and call themselves the Cutting Sword of Justice, infiltrate the computer networks of Saudi Aramaco, a Saudi Arabian oil company, and wipe out the hard drives of about 30,000 computers. Hackers left their calling card on each affected computer, displaying an image of an American flag on fire.

September

Nine banks in the U.S., including the Bank of America, Wells Fargo, and JP Morgan Chase, were hit by a distributed-denial-of-service attack that denied customers access to the banks’ websites for several days. The Islamic hacktivist group Izz ad-Din Al-Qassam Cyber Fighters (also called the Al-Qassam Brigades) takes responsibility for the attack. The group is linked to the military wing of Hamas.

October

U.S. Secretary of Defense Leon Panetta warns that the U.S. must protect itself against a “cyber Pearl Harbor.”

July

American officials announced that Chinese hackers had breached the computer network of the Office of Personnel Management in March. They said they believe the hackers were targeting employees applying for top security clearances.

November

The computer networks of Sony Pictures were hacked, with personal medical information about employees, financial information, emails, and thousands of other documents lifted and made public. The U.S. suspected North Korea was behind the breech in retaliation for the upcoming release by Sony of an outlandish comedy, called The Interview, about a CIA plot to assassinate North Korean leader Kim Jong-un. In December, employees of Sony received threatening messages on their computers warning that “the world will be full of fear” if the film is released. “Remember the 11th of September 2001,” a message said. Sony decided to cancel the release of the film. On Dec. 19, the FBI formally accused North Korea of launching the attack, saying it had significant evidence linking the government to the breech.

June

The White House said that the Social Security numbers and other personal identifying information of some 4 million current and former government employees had been breached. The breach occurred in late 2014. The data was accessed from the computers of the Office of Personnel Management. The government said it believes that the hack originated in China.