Link Trojan - Stealth Link Building

A link trojan is generally something useful that webmasters place on their site that then displays a link back. Wordpress themes are common link trojans. Mortgage calculators and download counters are classic link trojans.

It's not a voluntary vote for your site. So from a search engine's point of view it's not something they encourage.

This is not to be confused with a link condom, which is a link that has a nofollow on it to prevent it's vote from passing to another site.