>> Is it possible that there is something bad happening in the browser itself, confined to the local machine?
I'm laying bets on its something to do with the ad prefs which are stored as a cookie for each individual browser. Clearing cache and cookies should reset this, which is why J0hn's fixed when he cleared his cache.
What I dont know is how or why it shows those tesco ads (which arent really tesco ads). Ads served by google generally are supposed to be relevant to page content. The page content is quickly analysed and advertisers bid to display. All this happens rapidly. The reason I see VoIP or BT served ads is because they are relevant to content.
There is one other important setting (personal local machine settings) which I always have switched OFF and thats the "Interest based settings
". If its on, then it will pick up items that you may have previously searched for, or looked at.
This is why if youve been looking at new kitchen units, rather than display ads based on my site content, then you will be served an ad from someone like B&Q or whatever. That's nothing to do with me, its based purely on where you've been or what you've looked at some time in the past on some other site, and that's where the cookie is originally set.
Then when you visit some other site sometime later who serves google ads, then that will over-ride the site content based ads.
I dont understand the full workings - I dont think google discloses it, but what Im guessing is that somewhere along the lines something has been set for personal prefs. I tried my damndest last night to recreate it on both phones (one with Voda, the other EE, both galaxys) I switched off prefs and I even went to Tesco's hoping it would pick something up... but it didnt. This is why I strongly suspect that the cookie had originally been set from another site or a downloaded app.
Because its a cookie, then safe mode wont over-ride it. MBAM is designed to look for virus and exploits. This is just a damn annoying spam thing so unlikely to pick it up either.
Any other thoughts on where/how it could have been picked up appreciated.