Same as chazam ^^^^
First instance of it today. Web URL is mobprizes.com and the site header says 'Android Rewards'. Tried to browse XDA via Dolphin browser on Android and was auto-redirected to this spam page; you cannot press 'Back' or 'Exit' in the browser and have to click 'OK', whereupon another window opens asking you to enter your mob number (supposedly so they can contact you to sort out sending you your prize - which if you do a quick search on Google means you will receive plenty of premium rate text messages and no prize!).
Not sure what you folks can do but thought would mention it.
Incidentally, when performing a search re: this, one of the replies was on Yahoo Answers - when I clicked on this I was redirected to the same damn Android Rewards page!
I also noticed another forum in the search results is experiencing the same thing. Seems to be spreading.