A bug in Google's data processing code lead to a number of Blogger sites accidentally being labeled as spam, it has emerged.

According to Google, the bug caused the detection system to lock Blogger blogs that had otherwise passed the inspection by the company's spam algorithms.

"We are adding additional monitoring and process checks to ensure that bugs of this magnitude are caught before they can affect your data," the search engine said in a blog.

Google didn't immediately respond to a request for comment, so the scope of the problem isn't clear, but it apparently was significant, judging by the contriteness expressed in various official postings.

"We want to offer our sincerest apologies to affected bloggers and their readers," the blog said.

"At Blogger, we strongly believe that you own and should control your posts and other data. We understand that you trust us to store and serve your blog, and incidents like this one are a betrayal of that trust."

Google emailed publishers of the flagged blogs to notify them their sites had been locked after being classified as spam.

"To those folks who have received an email saying that your blog has been classified as spam and can't post right now, we offer our sincere apologies for the trouble," said another Google blog.

All blogs incorrectly flagged as spam have been reinstated, according to Google.

Blogger users began reporting the spam-identification problem early last week to the official Blogger Help Group, starting numerous threads about the issue.

The intensity of many of the complaints highlights the sense of helplessness individuals and businesses feel when a trusted technology provider fails them, even if the affected service is free, as is the case with the web-hosted Blogger publishing platform.

With the popularity of cloud computing rising, many users, from individual bloggers to large corporations, are increasing their use of web-hosted software, which offers a number of advantages but leaves them with little power to address outages or loss of data, since vendors have the applications in their servers.

Google's actions to clean up the Blogger platform no doubt respond to its broad misuse by scammers and malicious hackers to link to or distribute malware, a problem recently documented by internet consumer advocacy group StopBadware.org.

Scammers' exploit of Blogger made Google the owner of the fifth-largest malware-infected network in the world in May, according to StopBadware.org, which counts Google among its supporters.

In June, a Blogger bug affected publishers that post to their blogs via File Transfer Protocol (FTP).