The security lapse was traced to a handful of employees who visited a mobile software developer's website that had been compromised, which led to malware being installed on the workers' laptops. The PCs were infected even though they were supposed to be protected by the latest anti-virus software and were equipped with other up-to-date protection.
Facebook linked part of the problem to a security hole in the Java software that triggered a safety alert from the U.S. Department of Homeland Security last month. The government agency advised computer users to disable Java on their machines because of a weakness that could be exploited by hackers.
Oracle Corp., the owner of Java, has since issued a security patch that it says has fixed the problem. In its post, Facebook said it received the Java fix two weeks ago.
Facebook never mentioned the word "hack" in describing the breach. That, no doubt, was by design because hacking is a good thing in Zuckerberg's vernacular.
To most people, hacking conjures images of malevolent behavior by intruders listening to private voicemails and villains crippling websites or breaking into email accounts.
Zuckerberg provided his interpretation of the word in a manifesto titled "The Hacker Way" that he included in the documents that the company filed for its initial public offering of stock last year.
"The word 'hacker' has an unfairly negative connotation from being portrayed in the media as people who break into computers," Zuckerberg wrote. "In reality, hacking just means building something quickly or testing the boundaries of what can be done."