Two of our sites suddenly lose their first page positions for important keywords without no reason in one month successively. We believe some black hat hacker is doing this and I am very surprised why Google couldn't do anything against this attacks. Should we create a re-evaluation report on Google Webmaster Tools? What's your suggestion? We do not believe this is a natural search engine penalty occured by Google!
Well cant say its due to black hat hacking or some what similar. The reason behind this can be the updates to Google as to what it has launched regarding Content Farming and link Farming. Try keeping that in mind while going for preforming SEO....
Some time if you stop your onpage as well as offpage activity for a while then you should down in rankings just like that.. and for getting gain for continuous higher rankings you should concentrate on the seo of your websites and you need to enrich it with nice content... content farming is not at all allowed by google now a days...