I already gave a idea.
You have been hacked
Best bet is it is in one of your var### files.
So ftp to your UBBclassic\variables folder download all the files.
Then use a search method such as grep to search in each file for a string that matches such as "sexatcars"
It is the only way you are going to find it.
If it is not in your var files then you will need to expand to the other folders.
Or pay someone to find it for you.
BTW,
The site that was inserted in the iframe is blocked by my internet security as a dangerous site.
