It's a parameter in the Flash ad that tells it to sit in front of everything else on the page. The ONLY thing that I can do, in this case, is contact the ad network, who will hopefully contact the ad agency, who will hopefully contact the creative team that created the Flash ad, and request that they please modify it, and send it back to the ad agency, to send it back to the ad network.
I don't have the ability to. As soon as an ad behaves like this, all I can do is inform the ad network. If the ad network doesn't take immediate action (I give them about 24 hours), then, depending on my contract with them, I terminate all of the ads that I am currently running with them (which can be a substantial amount of revenue). Sometimes I'm not dealing with an ad network, but with an agency directly, and is often the case here my contract forbids me from taking the ad down under any circumstances.