If you’ve noticed your website suddenly drop in the Google rankings, you may have received a penalty for breach of Google’s guidelines. This penalty may be manually instigated in response to a complaint about your website or SEO activities, or it could be an automatic drop caused by a change in Google’s algorithm.
Algorithm Changes
When a website drops in rank because of an algorithm change, there’s usually a lot of others in the same situation. There’s no point complaining about it, you just need to work hard to find out what the problem is and change it. The good thing about an algorithm change is that once you figure out what the problem is and fix it, your ranking will recover quickly soon after the site is re-indexed. If you don’t do anything, the algorithm will continue to run and affect your site if you don’t change it to remove the thing that flags your site as “spammy”.
Manual Penalties
Websites can be penalized manually for a great number of things. They could get flagged for things like hidden text, content spam, javascript redirects, keyword stuffing or cloaking. This normally incurs a kind of “time-out” penalty for perhaps 30 days. More serious incursions of webmaster guidelines like cloaking, could incur a longer penalty. If removed, your site will eventually recover your ranking as it is re-indexed and deemed to be acceptable but durations vary considerably.
Reconsideration Requests
One option for faster recovery of your web ranking is a reconsideration request. Currently, if the penalty was manually applied, Google will consider your situation and the penalty may be removed. However, you’d need to have a pretty good idea of what was causing the penalty in the first place and then fix the site and ensure it doesn’t happen again.
View Google Engineer, Matt Cutts talking about recovering from a Google penalty in this video.