Seo problem - might relate to Penguin update

[VladTepes]

Penguin restricts further those crappy site contents and illegitimate backlinks. Aim more quality and relevant optimization for your site.

[steveschmidt85]

That drop might be mainly for penguin update also it can be for panda update as well(panda update happened after penguin but it affected very less sites). Do your link building in natural way

[AdamWill]

This thing is not happen only because of Penguin. Both Panda and Penguin did this all.

[Yondaime]

The dropped of rankings were caused by the updates of algorithm namely Google Panda 3.5 was on the 19th of April which targets the websites that aren't quality while Google Penguin was on 24th of April that is designed to target web spam pages like cloaking and keyword stuffing.

[nativetranslator]

Yes, Penguin update could be a reason for dropping such ranking. Now for all SEO it's essential to maintain quality link building, avoid over optimization of any website for SEO and stop repetition of using same anchor texts while posting.

[CertArt]

I too losing all good ranked keywords. Some are recovered too.

[Mispond]

I too losing all good ranked keywords. Some are recovered too.