Users of Twitter, Pinterest and Tumblr may have had their data compromised. 
The warning was issued following a breach to Zendesk, the company that supplied customers support service for all of the social networking companies.
Zendesk posted a blog about the breach, explaining that the company’s site had been hacked and it was possible that data from Twitter, Tumblr and Pinterest users may have been downloaded.
The blog, by Zendesk’s Mikke Svane, reads: “We’ve become aware that a hacker accessed our system this week. As soon as we learned of the attack, we patched the vulnerability and closed the access that the hacker had.
“Our ongoing investigation indicates that the hacker had access to the support information that three of our customers store on our system. We believe that the hacker downloaded e-mail addresses of users who contacted those three customers for support, as well as support e-mail subject lines. We notified our affected customers immediately and are working with them to assist in their response.”
The three companies have also alerted users about the data breach.