A script to redirect a variable percentage (eg. between 2-5% say) of visitors that land on the page to a link on placed on that page.
Because these links change continuously they need to be 'scraped' live from the actual page the visitor is on. And these links are placed on the page via javascript.
So for example:
We have '[login to view URL]'.
On '[login to view URL]' there are a list of links to external websites.
These list of links are displayed on '[login to view URL]' via javascript.
1 in every X visitors that land on this page are to be redirected to a random one of these links. (from a selection of up to 10 say.)
The remaining visitors that were not redirected stay on '[login to view URL]'.