The co-founder of Moz, Rand Fishkin, posted on Twitter and also on the Moz blog that one of the YouMoz, the user generated content portion of Moz, contributors received a Google Manual action for a link violation and it cited an article posted on YouMoz.
Here is the violation notice as posted by Rand:
So this goes back to guest blogging being dead for SEO purposes. Which concerned a lot of YouMoz contributors, but Moz reached out to Matt Cutts and he responded via email that Moz should be okay. Here is a snippet of the email:
That said, with the specific instance of Moz.com, for the most part it's an example of a site that does good due diligence, so on average Moz.com is linking to non-problematic sites. If Moz were to lower its quality standards then that could eventually affect Moz's reputation.
The factors that make things safer are the commonsense things you'd expect, e.g. adding a nofollow will eliminate the linking issue completely. Short of that, keyword rich anchortext is higher risk than navigational anchortext like a person or site's name, and so on."
In this case, the anchor text was indeed keyword rich:
But each and every YouMoz post is reviewed by someone at Moz, so Rand is upset about this.
Danny Sullivan on Twitter pulled out more questionable things about this guest blog post:
Forum discussion at Twitter.