TWITTER, Tumblr and Pinterest have been caught up in a hacking attack on a company that tech firms use to outsource their customer services.
Zendesk noted that a hacker downloaded email addresses of users who contacted those three customers for support, along with the email subject lines.
The company warned customers of the security breach in an email entitled: “We’ve been hacked.”
Some customers also may have had their phone numbers revealed, but no passwords were revealed, according to the website Wired.com.
Zendesk, which has more than 25,000 clients, uses software tools to allow companies to outsource a number of their customer service functions.
In an email to affected users, Twitter wrote: “Zendesk’s breach did not result in the exposure of information such as Twitter account passwords. It may, however, have included contact information you provided when submitting a support request such as an email, phone number, or Twitter username.”
Pinterest and Tumblr sent similar emails warning their potentially affected users.
This latest security breach comes on the same week that Burger King's Twitter account fell victim to hackers as it began sending out pro-McDonald's messages and the occasional rap video.
This latest security breach comes a week after Facebook revealed that it had been targeted in a "sophisticated attack" by hackers who exploited a previously unknown loophole in its computer system.
The social network insisted that no personal information of users had been compromised by the hacking attack.
It said that malware had infected its computer systems after employees had visited the website of a developer of mobile applications that was "compromised".
Apple computers were attacked by the same hacker, the company said in an unprecedented admission of a widespread cyber-security breach.
At the beginning of February, Twitter reported that 250,000 user details, including usernames, passwords and email addresses, were stolen by hackers. It said it was "not the work of amateurs".
The New York Times, Washington Post and Wall Street Journal have all accused China of attacking their computer systems.
Last week a report by US intelligence community concluded that the country was being targeted by a massive cyber-espionage campaign.