Google approach to webmasters is progressively changing and more often than not the Mountain View based company is warning webmasters regarding the possibility their site has been compromised? That’s right!
The search engine company sends a sort of warning notice that may be received either by emails or in the Google Webmaster Tools when it reasonably believe a site have spam-related issues that should be resolved lest the rankings to suffer.
Everything has started in early December, when Google started sending out notices regarding the existence of doorway pages. Then it was the time of the notification for selling links. Now, it appears Google is sending out notifications for buying links.
What should I have to look at?
The email template Google used looks pretty much the same like the old notification that was reporting "unnatural links on your site pointing to other sites”. The new phrase used in this circumstance is now “unnatural links pointing to your site".
Now, as the difference IMHO is not outlined properly, my recommendation is to read properly what the email says and takes action promptly.
Google often said competitors can't hurt your rankings; I don’t believe it as many other SEOers don’t. And in fact Google once admitted that anything is possible.