Google Docs, a web-based word processor, experienced a glitch that shared documents without permission.
The company issued a notice on the Google Docs Help Forum after a user noticed that all "collaborators" listed for a widely shared document were gone.
"The inadvertent sharing was limited to people with whom the document owner, or a collaborator with sharing rights, had previously shared a document," Jennifer Mazzon, Google Docs product manager, wrote on the official Google Docs blog.
Apparently, relatively few users were affected. Less than 0.05 percent of all documents were compromised, said Mazzon, and Google has apologised for the problem.
"We're sorry for the trouble this has caused," she wrote. "We understand our users' concerns (in fact, we were affected by this bug ourselves) and we're treating this very seriously."
The problem was fixed by an "automated process to remove collaborators and viewers from the documents that we identified as having been affected," Mazzon said, pointing out that some users would have to reshare their documents.
The incident caused some security observers to question the safety of web computing, especially from a corporate standpoint.
"This points up the real risks of cloud computing and data loss - how are users protecting their confidential data?" Dave Meizlik, director of product marketing at security firm Websense, told SCMagazineUS.com. "Users upload data as part of their job, but not necessarily with the sanction of IT."
One of the problems many IT administrators have with open cloud access is that it obscures IT visibility into what users are doing in the cloud, what data is going there, and whether some confidential data even belongs there, he said.
Google Docs is an on-demand application that saves files not to a user's desktop -- as is the case with programs such as Microsoft Office -- but to Google servers, so users can retrieve documents from anywhere using the internet.
Last September, a security researcher said he discovered a similar vulnerability in Google Docs that allowed private documents to appear in other users' accounts. Google later pushed out a fix.