Google's Eric Kuan from the Google spam team posted a response to one webmaster who said a competitor is spamming them with bad links and asked Google to provide examples of some bad links.
Eric did so in the Google Webmaster Help thread by showing a few links.
I always enjoy sharing these public examples because it gives those who have never received an unnatural link warning an idea of what links to stay away from. In this case, the webmaster is persistent about those links not being acquired by himself but a competitor trying to sabotage him.
Here are two of the links:
Here is the source code:
(a) The link in the source code actually reads rel=dofollow, really? DoFollow links in the HTML? That is asking for a Google review.
<a href='http://www.musiccenter.vn/2/13/Piano-cu.html' rel='dofolow'>dan piano</a>
(b) There are like 25 links in the footer all to their party web sites with anchor rich keywords.
(2) On forum.guitarpro.vn/showthread.php?t=29742 is a typical forum link with rich keyword anchors that everyone should avoid.
Google often goes after keyword rich forum, blog and footer links.
Forum discussion at Google Webmaster Help.