I have a site that has been up and running for approx 3 years but has recently been re-vamped and I have started SEO. The site was not in the first 10 pages before I started doing SEO. I have been optimizing the site since November with excellent results, I reached no.1 for several keywords and for all keywords managed to get page 1 to page 3 rankings. Then at the start of March, I was dropped for several keywords, last week they were back up and today they have been dropped again. I know that I have not been spamming and my rankings are increasing in every other major search engine.
Has anyone else had similar problems?
I have the "almost" same problem as yours. Our wordpress site was on the top 10 on major kw, but last month our main page was not even indexed but the sub-pages is there. I've checked our site using a cloaking detector and I have seen on the Google View that there are lots of drug/sex links on the footer area. It was being spammed!

I have found out that there are lot of sites having the same problem as mine, they called it Spam Injection or GORO hacking. I reviewed the codes, deleted the mysterious link and after a couple of weeks my index page is back! Thank God. I don't know how did they do it
