On January 1, 2014 Microsoft-owned Skype added itself to the list of high-profile Twitter compromised accounts. The company's Twitter account posted the following tweet:
As it can be seen, the tweet was even "signed" by the #SEA hashtag, which stands for Syrian Electronic Army. SEa is a group of hackers that support the Syrian regime, which has been responsible for previous high-profile Twitter hacks. The tweet states "Don't use Microsoft emails(hotmail,outlook). They are monitoring your accounts and selling the data to the governments. More details soon #SEA". Basically a classical case of political hacktivism.
The tweet looks anomalous at first sight, not only for the odd content sent out by the account of a Microsoft-owned Twitter account, but also for the hashtag that attributes the tweet to the middle-eastern group. However, Twitter's automated defenses did not block the tweet as anomalous. Even worse, since the compromise happened on a holiday, it took Microsoft hours before the tweet was taken down.
It is to detect and prevent such incidents that we developed COMPA. COMPA learns the typical behavior of a Twitter account, and flags as anomalous any tweet that significantly deviates from the learned behavioral model. My colleague Manuel Egele and I checked the malicious tweet by the Syrian Electronic Army against the behavioral model built for the Skype Twitter account. The result is positive: had it been deployed on Twitter, COMPA would have detected and blocked the tweet, and saved Microsoft some public relations embarrassment.
More in detail, the Skype twitter account always posts from the Sprinklr Twitter client, while the malicious tweet was sent by the regular Twitter web interface. This fact is already very suspicious by itself. As a second element, the Skype Twitter account never used the #SEA hashtag before. In addition, the malicious tweet did not contain a URL, which is common practice in Skype's tweets. Interestingly, the time of the day at which the tweet was sent matches the typical sending patterns of the Skype Twitter account. However, this was not enough to evade detection by our system.
This result shows that COMPA is effective in detecting and block tweets that are sent by compromised Twitter accounts. We strongly advocate that Twitter and other social networks implement similar techniques to keep their accounts protected, and block malicious tweets before they are posted.