Facebook has announced it was the target of hackers but that no user information was compromised during the attack.
The social media giant said on its security blog that the company discovered in January that its system had been targeted in a sophisticated attack.
The attack occurred when a handful of the company's employees visited a developer's compromised website, which led to malware being installed on their laptops.
Facebook said it has found no evidence that user data was compromised.
The company has fixed the infected machines, informed law officials and an investigation is under way.
Facebook also said it was not the only company targeted in the attacks but was one of the first to discover it.
"We are working continuously and closely with our own internal engineering teams, with security teams at other companies, and with law enforcement authorities to learn everything we can about the attack, and how to prevent similar incidents in the future," Facebook said on its website.
Amazon selling rape game http://tinyurl.com/bb9p9j— Belfast Telegraph (@BelTel) February 12, 2009
Dia daoibh gach duine, I am now on twitter.— Gerry Adams (@GerryAdamsSF) February 6, 2013
Testing... testing... Is this thing on??— Tom Hanks (@tomhanks) January 11, 2010
Thinking we're only one signature away from ending the war in Iraq. Learn more at http://www.barackobama.com— Barack Obama (@BarackObama) April 29, 2007
Greetings Tweetarians! I have just landed on your Planet. This could be my last Tweet.— Jerry Seinfeld (@JerrySeinfeld) July 15, 2011
Tis my first twitt-er. Or tweet? Twit? Or tweet? "Twit or tweet everybody." Is this anything?— Ellen DeGeneres (@TheEllenShow) March 10, 2009
Warren is in the house.— Warren Buffett (@WarrenBuffett) May 2, 2013
It’s cold and will only get worse but at the moment it’s bearable. Holly and Sam are coping well as are the rest of the crew.— Richard Branson (@richardbranson) October 22, 2008
New: Peter Robinson Official Twitter Site. Messages begin on Monday.— Peter Robinson (@DUPleader) April 2, 2011
Very windy at cog hill today! Only managed 5 holes this morning. Hopefully it will be a little better for the pro am tomorrow.— Rory Mcilroy (@McIlroyRory) September 7, 2010
First tweet. Happy birthday Loretta Lynn. gL.x— gary lightbody (@garysnowpatrol) April 14, 2012
Zoe Salmons Official Twitter account- trying to get the other taken down!— Official Zoe Salmon (@Zoe_Salmon) May 19, 2009
I am currently talking about twitter— Pete Snodden (@PeteSnodden) March 4, 2009