Historically (years ago) it was widely exploited, but in the past two years it's had fewer exploits than either Chrome or Firefox. Plus it doesn't install unsecure toolbars or Java by default, when it updates. Plus in a corporate setting IE can be managed by policy and centrally updated, whereas Chrome and Firefox can't be. Firefox is even worse than Chrome in this regard because when it is updated for one user on a computer, it is not updated for other user profiles on that system – i.e. all profiles on the front desk computer, the conference room computer or shared admin/spare computers.

Think big picture. In 2013 IE had HALF the number of vulnerabilities than either Chrome or Firefox.

http://secunia.com/vulnerability-review/vulnerability_update_top50.html

I expect Microsoft will rush out a fix for this particular issue, and for people who update it will be fixed. There are also restrictive settings that could be activated immediately to mitigate the current vulnerability. Start by disabling the Adobe Flash plugin. Go to Tools-Manage Add-Ons, select the Flash line-item, click "disable". That will stop the known exploit for now, although it doesn't fix the bug.