Brilliant CharleyO,
Very good find and proof that you do your link-checking like it should, the site you mentioned, will indeed infect with a IFrame exploit, see the DrWeb's AV-hyperlink checker plug-in info:
Checking: hxxp://thenelsonbrothers.com/
Engine version: 4.44.0.9170
File size: 3154 bytes
hxxp://thenelsonbrothers.com/ - archive HTML
>hxxp://thenelsonbrothers.com//JavaScript.0 infected with Exploit.IFrame
>hxxp://thenelsonbrothers.com//JavaScript.1 - Ok
polonus