The Inside Facebook blog reported earlier today that the social networking site temporarily blocked URLs shortened with the ow.ly domain developed by Vancouver's HootSuite. According to Inside Facebook, the blocking was in response to a worm distributed in an ow.ly link.
The worm’s shortened URL contains the Facebook query string “?=www.facebook.com/photo.php” which could fool users into thinking they were visiting a Facebook page. All Ow.ly links on Facebook, legitimate and malicious, temporarily led to Facebook’s blocked abusive site error page.
Facebook explains the blocking as a response to spammers trying to hide malicious links behind URL shorteners and states that in rare cases they may temporarily block all use of a specific shortener.
We asked HootSuite CEO Ryan Holmes for a comment and he responded that they are "aware of the situation with Ow.ly links and have reached out to Facebook. They are investigating the cause of the conundrum and we expect to have a solution soon."
Incidentally Facebook is a HootSuite user - twitter.com/facebook.