http://en.wikipedia.org/wiki/LinkedIn

LinkIn is a business-related social networking site.

Easiest way to block them is mark all mail from them as SPAM and your provider should just toss it into the junk bin. Or if you have one that allows filters, you can do the same thing.

block linkedin.com

All it is, is people you know, or someone who has you in their email list, who want you to join them on that network.

I'm a member because people kept sending me invites and I don't know why because I never look there.