March 30, 2012 at 5:36 PM ET
Updated, 11:15 pm PT: An app developer named Geoff Evason tweets that he found a bug in Twitter's TweetDeck software that "has given me access to hundreds of accounts." About an hour and a half later, the client software stops working. The official message: "TweetDeck is currently down while we look into an issue. Apologies for the inconvenience."
It remained that way for several hours.
"I didn't hack TweetDeck or find an exploit," said Evason, in an email to msnbc.com. "I just logged in and was presented with lots of accounts that weren't mine."
Evason, who lives in Ontario, Canada, said he sent "two simple 'test' tweets, so I could add more info in my report to Twitter, but didn't feel it was appropriate to do anything more than that."
He also posted a picture of the accounts he had access to (shown here, at left): "The 'blue' accounts are selected, and the white ones are not," he said. "TweetDeck lets you connect multiple Facebook and Twitter accounts. Normally I manage four accounts in my TweetDeck. For any given post you can select what accounts you want to the update to be posted to.
"Originally, when I first saw what was going on, I was going to post from as many of the accounts as I could (hence why so many of the ones in the picture are blue). I quickly realized that was inappropriate."
Twitter bought TweetDeck last year. The program lets users customize Twitter even more, so that tweets can be scheduled for release, for example, or various feeds arranged in customizable columns.
The outage for TweetDeck does not mean that Twitter itself is out. Twitter users who rely on TweetDeck may still go to twitter.com, which was functioning normally when this was published.
Update: After about 8 hours offline, TweetDeck "is now back online," a Twitter spokesperson told msnbc.com. The problem was "a bug that caused a very small number of TweetDeck users to have access to other TweetDeck users’ accounts ... No one's password was compromised, and we aren't aware of any instances where this access was used maliciously. As a precaution, we removed account credentials associated with affected TweetDeck users; they will need to log in to authorize the TweetDeck application to access their accounts."