Is Site Advisor have the same function as a link scanner?

I was listening to a pc/digital radio talk show and the host suggested installing a link scanner.  I ran a Google search to define what a link scanner is and from I read it's similar to Site Advisor.  I already have that application.  What I thought a link scanner function does is scan links sent in emails, but that might not be accurate.  Just what does a link scanner do? 

 

The second question I have is if NIS scans emails for viruses, does it scan links sent in emails?  Especially those "forwards" from friends.