I mean ads that use JavaScript to automatically open app stores without the user actually clicking on an ad, just by viewing a page.

I'm seeing this practice increasing and spreading. It must be effective.

I've seen it on some big web properties. The other day I was browsing the Guardian and boom, iTunes opened. If spent some time afterwards on my PC and Fiddler duplicating the views using a faked user agent to watch the redirects and cookies. It is slyly done. Normally it only happens once per session. They drop a cookie so that they don't persistently annoy the user, just once in a while.

There have been ads getting through some of the exchanges that automagically open the AppStore or iTunes without you clicking or tapping anything...