Twitter has been hit by an avalanche of malicious tweets that are being sent by thousands of compromised user accounts. The ongoing attack, which was about two hours old and showed no signs of abating as this post was about to go live, appeared to be linked to security breaches affecting third-party sites and apps. Early on, every single one of the tweets viewed by Ars contained the tag “via weheartit.com,” prompting speculation the compromised Twitter accounts were linked to the social network by that name, which hosts services for image sharing and promotion. Later on, however, tweets that were part of the same campaign carried tags showing they were transmitted by apps such as the Twitter for iPhone, making it unclear exactly what was the source of the non-stop torrent.