View Source reveals porno links in my customers site

I can't publish the url here, as it will be searchable, but I was updating my customer's web site today and in IE 7 I went to View Source, LIsted under my normal code are a couple of hundred links to porno sites.

Here's an example:
href="http://zgrade.com/alenaprosti=302">free teen porn dirty</a><a

There is a js menu in there that I created with Likno's "AllWebMenu5", for what it's worth.
I realize this is very limited information and I will be happy tp provide more; I'm concerned about somebody coming upon this post while searching for my customer.

I'd like to find out how this could have happened, how to fix, and how to prevent it in the future.

Thanks for any help!
Brian