Help with Tumblr pop up?

[Shiloh]

Hey so I've had a tumblr for a couple years now, but recently I've got a virus on my blog I think. Whenever I go to my blog, whether im logged in or not, an ad with pop up in another window specifically an Adfly pop up. Why? How do I fix it? Its only when I type in my blog url that I get that pop up. My laptop doesnt have a virus (I have Norton Anti-Virus and it says my laptop's clean). Do you think I should change my blog theme? Maybe a virus has changed my html code to allow a pop up every time? Idk. It's only when I first type in the url. If I close it out and visit my blog later there is no pop up. And this isnt the first time it's happened - it's happened over 6 times. Argh its driving me insane.

Thanks for your help

[NortonSupport]

Hello,

Sorry for the trouble. Can you please enter your blog url in the safe web rating field and see what the rating is: http://safeweb.norton.com/

Let me know if that helps!

Thanks!

Vineeth
Norton Support

[Stone]

If you had provided the link, I could have checked your source code.

I suggest going to the theme revert page:
http://staff.tumblr.com/post/380346543/theme-recovery

See if reverting theme to an earlier time fixes.

Then change password.