seb86/AffiliateWP-Banners-Widget — pull request #3 by samuelaguilera (2014-06-01 20:59:56+00:00)
Title: Affiliate links should have rel="nofollow"

Affiliate links should have rel="nofollow" to comply with Google quality guidelines.

http://www.youtube.com/watch?v=F0LJwwTxJVo

Also affiliate links can be considered paid links, and paid links must contain rel="nofollow" to avoid penalizations in your domain (and linked domain) from Google.