It just happened again:
http://imac.ios.iv.qs.c.hoskbkkcm.com/FPlayer/UKXIND/auload.html?installer=Flash- _Player_17_for_Other_Browsers&browser_type=KHTML&dualoffer=false

I didn;t see what the ad was, because I'd scrolled down and a popup message appeared, which stopped me scrolling back to see the ad.