I was hit by PANDA in October. I worked hard to correct anything that seemed to caused the issues only to find out in April that i was hit again. And now on the 8th June i got hit again. Now i don't know what to do, cause none of the changes seem to have any effect whatsoever.
I have several concurrency sites, none of them suffered, and now all of them are better ranked than me, despite the fact that i can point out at least 10 crucial problems which do not abide by the rules(suggestions) of google.
All in all i'm now down by 60%.