Would it be ok if you can provide a screencap of it when you click an ad again? Does it appear only in ClixSense, or while you surf and use on other sites?
Meanwhile, in any case -- try to do a full scan with an anti-virus and
an anti-malware program*
* Please don't run both at the same time; it'll make the detection of whatever's in your gear inaccurate
-- do this after you have safely logged out of your online accounts ( allocate at least a couple of hours when doing a Full scan for both programs )