If you still use Internet Explorer, there's more to worry about than a crappy browsing experience. Microsoft has confirmed that it's looking into a "mouse tracking" flaw which affects IE 6 through 10.
The security problem was identified by a group called Spider.io earlier this week. It claims that versions 6 through 10 of IE are capable of tracking cursor movement even when the browser window is inactive, unfocused or minimised — and that malicious ads could abuse that ability to track your mouse movements.
Indeed, Spider.io has shown that it's possible. It's not clear how useful the resulting data is — mouse clicks can't be recorded, for instance — but it should still be of concern to those worried about software security. Microsoft claims to be "actively working to adjust this behaviour in IE". [The Verge, Spider.io, Microsoft]