Web users trying to view content on Twitpic, or even Twitpic's own Twitter account, instead got a grim message from Google, News.com.au reports.
"Content from Twitpic.com, a known malware distributor, has been inserted into this web page. Visiting this page now is very likely to infect your computer with malware," the notice said.
According to the report, Twitpic, which has over 35 million users, tweeted the problem had been resolved.
The report said that it is unclear whether Twitpic posed a legitimate security threat to users, or if the block resulted from a glitch in Google's malware detector.