How can I get more credits?

Complete noob here, my PS3 is not jailbroken but I'd like to get more credits on gt6 without spending countless hours racing....what can I do to get millions of credits? I have found some sites online that claim to add unlimited credits somehow when you download their program, but can't see how this works...sites like undectedcheats.com.
Don't want to get scammed, so figured I'd ask on this forum because it seems legit.
Thanks