Recently I have seen an uptick in reports of individuals taking advantage of the Penguin and other updates to destabilize the rankings of their competitors.
This is an old school method called Google Bowling. It’s when you point large amounts of low quality links to a competitor in a fashion that looks like that competitor is the one that purchased those links. Hence tripping off all sorts of spam filters within Google and penalizing that targeted site.
It’s been done to bury competition in the past, but only recently it appears to be more effective to the point where in a test environment I was able to bury a website in the rankings using only external links, and trust me.. not many were needed. Took a whopping 3 minutes to allocate the proper links to bury it.
Scary, I was able to send that many links to my own test site to cause that error to appear, and see the targeted site go down in flames.
Next thing I am waiting is to get a call from companies asking me to bury their competitors.
A notice showed up on the targets webmaster tools saying
Google Webmaster Tools notice of detected unnatural links to XXXXXXXXX
Dear site owner or webmaster of XXXXXXXXXXX
We’ve detected that some of your site’s pages may be using techniques that are outside Google’s Webmaster Guidelines.
Specifically, look for possibly artificial or unnatural links pointing to your site that could be intended to manipulate PageRank. Examples of unnatural linking could include buying links to pass PageRank or participating in link schemes.
We encourage you to make changes to your site so that it meets our quality guidelines. Once you’ve made these changes, please submit your site for reconsideration in Google’s search results.
If you find unnatural links to your site that you are unable to control or remove, please provide the details in your reconsideration request.
If you have any questions about how to resolve this issue, please see our Webmaster Help Forum for support.
Google Search Quality Team