This latest security breach at Zendesk is said by the company to have affected three of its top clients, namely Twitter, Pinterest and Tumblr.
The Zendesk breach comes after a recent spike of attacks on major and well known technology companies like Apple, Twitter and Facebook.
All three technology companies revealed that their employees’ computers had been hacked and fallen victim to “unauthorized access”.
Zendesk said: “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 email addresses of users who contacted those three customers for support, as well as support email subject lines. We notified our affected customers immediately and are working with them to assist in their response.”
Experts believe the attackers could use the stolen information in “social-engineering attacks”.
Zendesk said it discovered the cyber attack last week and promptly patched the vulnerability.
The statement added they were “incredibly disappointed” by the incident and said they had “already taken steps to improve our procedures”.
It concluded: “We are also completely committed to working with authorities to bring anyone involved to justice and make certain we fully understand what happened.
“As this process unfolds, we aim to update our customers in as transparent and timely a manner as possible about new developments.”