Private computer service provider Zendesk acknowledged that its site was the victim of a cyberattack, which allowed hackers access to confidential customer data for Twitter, Tumblr and Pinterest, all popular websites. The San Francisco-based company said “it’s working to address the issue,” but it didn’t offer further details.

“As soon as we learned of the attack, we patched the vulnerability and closed the access the hacker had,” Zendesk announced. The attackers were able to download customer email addresses and subject lines of emails.

Earlier Friday, the Department of Homeland Security posted a warning about “ongoing malicious cyber activity” against the U.S. government, as well as many private enterprises. “The apparent objective of this activity has been the theft of intellectual property,” the warning said. Other data sought includes intellectual property, trade secrets and sensitive business information.

The department urged network administrators to contact it for more information. The posting came after computer security specialist Mandiant, a contractor to New York Times Co. (NYSE:NYT), published a report linking a unit of China's People's Liberation Army to cyberattacks on U.S. sites.

The website also said it was “working with authorities to bring anyone involved to justice.” 

Separately, Twitter, Tumblr and Pinterest notified customers of the attacks. The sites said they didn’t believe other confidential data like passwords had been compromised, although some phone numbers may have been accessed.

Zendesk’s announcement comes in a week when major consumer sites including Facebook (NASDAQ:FB) have acknowledged cyberattacks. Others, including Apple Inc. (NASDAQ:AAPL) and Google Inc. (NASDAQ:GOOG)  have reported being cyber targets as well.

Apple released a patch late Thursday for its Java OS X Lion and other software. Google released a patch to Google Chrome that it said could handle vulnerabilities.

Zendesk was established in Denmark in 2007 by programmers headed by CEO Mikkel Svane seeking to offer one of the first cloud-based services.

Last year it raised $60 million in new venture capital from Redpoint Ventures, Index Ventures, Matrix Partners, Charles River Ventures and Benchmark Capital and GGV Capital as well as from Goldman Sachs (NYSE:GS). It took in $6 million in initial funding in 2009 from Benchmark and Charles River.