April 24th 2012 was when Google released a change to their algorithm, this was named "Penguin" and was said to target sites who are over optimizing or spamming in order to manipulate the SERP's (something we all do to a certain degree).
Google Webmaster Blog:
“The change will decrease rankings for sites that we believe are violating Google’s existing quality guidelines. We’ve always targeted webspam in our rankings, and this algorithm represents another improvement in our efforts to reduce webspam and promote high quality content. While we can’t divulge specific signals because we don’t want to give people a way to game our search results and worsen the experience for users, our advice for webmasters is to focus on creating high quality sites that create a good user experience and employ white hat SEO methods instead of engaging in aggressive webspam tactics.”
What does the Penguin target?
- Paid text links using exact match anchor text
- Comment spam
- Guest posts on questionable sites
- Article marketing sites
- Links from dangerous sites
I think some more research is needed before anyone makes a judgement call on the real reason why there website has taken a hit!!