(Bloomberg) — Twitter Inc. has notified some users that theiraccounts may have been hacked by state-sponsored actors, as thecompany works to investigate the attack.

"We believe that these actors (possibly associated with agovernment) may have been trying to obtain information such ase-mail addresses, IP addresses, and/or phone numbers," Twitterwrote in an e-mail sent on Friday.

Tech companies have been stepping up their efforts to deal withhacking threats. Facebook introduced a new system ofnotifying people of suspected attacks in October, and Google hasissued security warnings in the past. Twitter didn't say in themessage what countries may have been behind the latest attempts toaccess the accounts, some of which were owned by users involved insecurity and free speech.

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"There are a fair number of countries not fond of journalists,dissidents, free speech in general," said Steve Bellovin, acomputer-science professor at Columbia University. "I suspectthey're looking for direct message traffic within Twitter."

Nu Wexler, a spokesman for San Francisco-based Twitter, didn'timmediately respond to a request for comment.

The e-mail from Twitter included links to the Tor Project and anElectronic Frontier Foundation website on safety when using socialnetworks. Runa Sandvik, a privacy researcher, said that the e-maildidn't offer users much information to effectively protectthemselves.

"It doesn't say what I should do next — should I changemy password? My e-mail address?" Sandvik said. "I'm hoping thatTwitter is spending the resources that it needs to actually lookinto this and figure out what happens."

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