More Fun and Games to be Certain I Never Get Bored

[eshrink]

I logged onto my homepage (a vBulletin 4.15PL1 CMS), and Microsoft Security Essentials warned that MY site had infected me with:

Trojan:JS/Iframeinject.M

It infects me (and anyone else) who goes to the site at http://www.mywebsite.com.

If you go to http://www.mywebsite.com/forums/index.php, this does not occur nor does it for the blog etc.

I looked at .htaccess but there is nothing pointing.

The name of the trojan sounds as though it has injected its nastiness via iFrame.

Anyone have suggestions as to finding how this is being done. I have not used M$ Security Essentials prior to today after removing Norton's Internet Security. Thus, Norton's may have missed it (unlikely) or it was introduced between deleting Norton's and adding Security Essentials.