Twitter says it has fixed a hacking problem.

The short-messaging service announced the fix this morning after mysterious "tweets" of blocked-out text propagated themselves and caused popup windows to open.

Twitter now says the attack has been "fully patched" and no longer works.

The hack had been extra-nefarious, because the tweets activated without being clicked on — it was enough for web surfers to move their mouse cursors over them.

The hack only affected visitors to Twitter.com, however.

Various third-party programs used to send and read tweets were unaffected.