Zendesk says breach compromised email addresses

Zendesk said Thursday a hacker gained access to support information for some customers of its online help desk software.

"We've become aware that a hacker accessed our system this week," wrote Mikkel Svane, Zendesk's CEO. "As soon as we learned of the attack, we patched the vulnerability and closed the access that the hacker had."

The company has more than 20,000 customers, including large enterprises such as Sears, Xerox and Groupon. Svane wrote that the three affected customers have been notified, but he did not identify the businesses. However, Twitter wrote that it was "emailing a small percentage of Twitter users who may have been affected by Zendesk's breach. No passwords involved."