We’ve noticed some highly targeted and apparently politically motivated attacks against our users. We believe activists may have been a specific target. All these attacks abuse a publicly-disclosed MHTML vulnerability for which an exploit was publicly posted in January 2011. Users browsing with the Internet Explorer browser are affected. We’re working with Microsoft to develop a comprehensive solution for this issue. For now, we recommend users and corporations seriously consider deploying Microsoft’s temporary Fixit to block this attack until an official patch is available.
Source: https://thehackernews.com/2011/03/mhtml-vulnerability-under-active.html