Panda audits
 

Best advice I can give you if you have been hit by Panda is to review your site logs against the listed updates. If there is a correlation then bingo, you know what the issue is.

Panda audit enables a website administrator to do four things:

1.Gather data
2.Evaluate pages to determine what to keep, what to modify, and what to throw away
3.Perform a technical audit based on observations gained from the use of webmaster tools
4.Optimize every page for Google’s standards

Panda-proof content audit for your site - all you need to know to make sure your content matches Google's quality criteria.