Safari Virus Pop Up Closes App

Usually shortly after loading Safari it says: "Congratulations! Safari is now up to date! Click Close to continue". It closes and when I reload Safari it is in a small rectangular shape and the page is set to some "extensions page" which I assume is fake. I can hit my home button back to yahoo and it all seems fine. Also, it keeps popping up a new tab about the need for virus protection. I close that out before it loads and it stops for a while but keeps doing it periodically. Please help. Thanks.