"We believe Google Apps and related customer data were not affected by this incident," Google Enterprise President Dave Girouard wrote in a .

The company said in a Tuesday that the attack had resulted in the theft of some of its intellectual property, but that it appeared to have been designed primarily to access the e-mail accounts of Chinese human rights activists.

It also said that, as a result of its investigations, it discovered that at least 20 other large companies from a wide range of businesses were similarly targeted.

"This attack may understandably raise some questions, so we wanted to take this opportunity to share some additional information and assure you that Google is introducing additional security measures to help ensure the safety of your data," Girouard wrote, without specifying what Google will do differently.

He reiterated Google's mantra for cloud computing and Web-hosted software -- that while no one is immune to malicious hackers, Google is able to keep data safer than the average corporate IT department.