( CNN ) -- Customer support tool Zendesk announced in a blog post Friday that it had been hacked earlier this week . The hack affected users of three services that use Zendesk : Pinterest , Tumblr and Twitter . `` We believe that the hacker downloaded email addresses of users who contacted those three customers for support , as well as support email subject lines , '' Zendesk said in the post . It did not name the three customers publicly , but subsequent e-mails from Pinterest , Tumblr and Twitter to their customers confirmed the breach . `` We recently learned that the vendor we use to answer support requests and other emails ( Zendesk ) experienced a security breach , '' said Pinterest in an email . The pinboard-style photosharing social network site said it was only sending the e-mail to people who had used Zendesk and were possibly compromised . It urged users to take measures to keep their accounts secure by not sharing their passwords and using strong passwords . Tumblr told its customers to review any e-mail conversations they had with Zendesk to make sure there was no account information that could be used in phishing attacks . CNN 's Heather Kelly contributed to this report .
The sites were breached via their vendor , Zendesk . Comment: The company urged users to ensure their passwords are strong .