Last month several sites reported that Google has implemented a minus six (-6) over-optimization penalty.

Many sites occupying the highly coveted No.1 position for a particular query suddenly find themselves at number 6. (Which, of course, means that this is really a minus 5 penalty, but that is not important.)

The explanation given by Planet Ocean is that Google thinks that your search engine optimization efforts are looking a little too efficient—and that they are implemented for the sole purpose of manipulating search rankings upward.

Many of these sites have highly optimized pages tightly focused around a single core phrase or keyword, Planet Ocean argues.

Google now argues that the effect was caused by a glitch in the system and that an attempt to filter out bad sites had caught good sites in the process. Most sites should get their original rankings back soon.

See also: It’s Official, Position 6 Penalty Is Now Receding! (PageTraffic Blog)
Google’s Mysterious Position Six Penalty (Search Engine Land)