Facebook founder Mark Zuckerberg briefly found his Twitter account had been hacked, as were at least two of his other social media accounts.
Zuckerberg's Facebook account and password were not compromised, the company said in a statement; his account on Facebook-owned Instagram was also unaffected.
Facebook Inc said on Monday morning that none of the company's systems or accounts were accessed and that Zuckerberg's affected accounts have since been re-secured.
A person close to the situation confirmed that Zuckerberg's LinkedIn and Pinterest accounts also were affected. Officials for both of those social media networks did not immediate respond to requests for comment.
Screenshots preserved by the technology website Engadget appeared to show someone with access to his largely dormant Twitter account, using it to say Zuckerberg was "in the LinkedIn database" and inviting the social media mogul to get in touch. LinkedIn declined to comment.
It is not yet clear how the hack happened, although a spate of massive data breaches at companies - along with recent news that a 2012 breach at LinkedIn Corp was much bigger that previously disclosed - has recently given hackers a wealth of password data to work with. Several high-profile Twitter users have also had their accounts hacked in recent weeks.
Zuckerberg's name is synonymous with Facebook, but the billionaire has several accounts on rival social networks, including one registered with Google Inc. None appear very active.