"Spear-phishing" typically works by sending fake e-mails that look like legitimate correspondence, but which link to a malicious website or file attachment.

BBC: The White House as seen on 17 March 2010

The most common threat was a technique known as spear-phishing, which can corrupt a company's computer system by uploading malicious attachments and gaining access to sensitive information.

CNN: Homeland Security cites sharp rise in cyber attacks

Recent attacks that have hit Apple, Facebook and other high-profile companies often bear similar hallmarks of infiltrating a system via employee computers, and with a straightforward spear-phishing campaign.

FORBES: Apple Admits To Being Hacked, Says No Data Stolen

The rise of social networks, for example, has aided an increasingly common kind of attack known as spear-phishing, says Greg Bell, global service leader for KPMG's information protection practice.

WSJ: Tech Companies Struggle to Keep Hackers at Bay

Much of the campaign involved sending spear-phishing emails, where an unsuspecting target would click on a link, activating a program that would then runs quietly in the background of their computer network.

FORBES: China Thought To Be Behind Global Cyber-Espionage Campaign That Hit UN, Olympic Committee

Many highly publicized attacks have been based on a tactic called "spear-phishing, " where email users are tricked into opening a legitimate-sounding message that contains code called malware that lets attackers penetrate corporate networks.

WSJ: Apple Hit by Hackers Who Struck Facebook

They have not been able to establish how exactly the hackers broke into the system, but believe it may have been through a so-called spear-phishing attack, where an employee clicked on an email or link containing malicious code.

BBC: New York Times 'hit by hackers from China'

The new breed of spear-phishing emails appear to be sent by a close friend or family member, address the victim by name in the subject line or body of the message, and include a link to a website controlled by spammers.

FORBES: Facebook Says 'Misconfiguration' Allowed Spammers To Impersonate Users