Generally that sort of pattern is used for measurement purposes. For example that technique is often used to measure affiliate links. Indi, it's this: If you look at the form the footer links take on
this thread they're not regular anchors going straight to the link but instead this pattern, going via the forums:
/forum/redirect-to/?redirect=http%3A%2F%2F URL
Not sure if I'm making a great deal of sense but have a look through the source of that thread and you'll see what I'm blethering on about. Basically there's then also something behind the scenes which makes that URL to redirect to actually go to the URL. But the advantage here for the webmaster is that it makes it
measurable. It is generally difficult to measure exits
out from a website otherwise. And it's the same in all the private forum posts - done programatically. Ie something like "if post is in form x then change footer links into this forum". It's also a perfectly ok thing to do - those private forums are excluded from robots anyway