"We've been hacked," said Zendesk CEO Mikkel Svane Thursday in a blog post. Zendesk offers cloud-based help desk software and hosts customer support portals used by numerous businesses. Accordingly, the hack puts Zendesk's customers' personal information at risk.
"We've become aware that a hacker accessed our system this week," Svane said, without specifying the length of time that attackers had access to Zendesk's site. "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," he said.
[ Could your users be at risk from another high-profile hack? See NBC Websites Hacked To Serve Citadel Financial Malware. ]
Zendesk didn't name the three affected customers, which it said knew nothing about the breach until being so informed. But Twitter and Tumblr were quickly identified as being two of the affected businesses, due to warnings they emailed to their own customers. "Emailing a small percentage of Twitter users who may have been affected by Zendesk's breach. No passwords involved," read a tweet to Twitter's support channel posted Thursday.
Twitter's email to users warned that some user information may have been stolen. "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," read Twitter's email to affected customers. "We do not believe you need to take any action at this time but wanted to ensure that you were notified of this incident."
The breach of some Twitter user data marked the second security breach to have affected Twitter users in two months, following the compromise of about 250,000 Twitter users' accounts. It also followed this week's high-profile hijackings -- by unknown hackers -- of the Burger King and Jeep Twitter accounts.
Tumblr, meanwhile, emailed customers to warn them that it's used Zendesk for more than two years, and that any customers who emailed Tumblr support in that time may be exposed, and had their email addresses and email message subject lines stolen by attackers. "The subject lines of your emails to Tumblr support may have included the address of your blog which could potentially allow your blog to be unwillingly associated with your email address," said Tumblr.
Stolen information might be exploited via social-engineering attacks. On that front, Tumblr advised users to beware potential phishing attacks disguised as official Tumblr communications. "Tumblr will never ask you for your password by email. Emails are easy to fake and you should be suspicious of unexpected emails you receive," said the company.
By late Thursday, the final affected Zendesk customer was publicly identified. "And we have a winner! Joining Tumblr and Twitter in the ZenDesk breach is Pinterest! Now if they would say how they got in ..." tweeted the threat intelligence manager for Trustwave SpiderLabs, who goes by "Space Rogue."
Pinterest likewise sent an email -- subject: "An important notice about security on Pinterest" -- to affected users. "We're sending you this email because we received or answered a message from you using Zendesk," it read. "Unfortunately your name, email address and subject line of your message were improperly accessed during their security breach." The email called on users to beware suspicious emails, and while it didn't suggest that any user passwords had been obtained, it recommended always using strong Pinterest passwords. "Hackers can sometimes guess very short passwords with no letters or symbols. If your password is weak, you can create a new one," read the email.
"We're really sorry this happened, and we'll keep working with law enforcement and our vendors to ensure your information is protected," it said.