Changes to Google's Algorithm To Prevent Spam
Matt Cutts had mentioned earlier this month on http://googleblog.blogspot.com/2011/01/google-search-and-search-engine-spam.html – “we’re evaluating multiple changes that should help drive spam levels even lower, including one change that primarily affects sites that copy others’ content and sites with low levels of original content.”
He confirmed on his personal blog http://www.mattcutts.com/blog/algorithm-change-launched/ that the Google Algorithm has been updated and live now to prevent content spam.
Matt Cutts has also posted about this update on http://news.ycombinator.com/item?id=2152286
Before this announcement also there were many SEOs who were discussing about the effect on the SERPs http://www.webmasterworld.com/google/4258897.htm