My search engine traffic volume stopped growing on the day my server was hacked. No idea if the two are related, but looking at the chart it certainly looks suspicious.
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I had heard that there was a google Panda update around that time, but according to this Penguin&Panda calendar, that’s not correct. March 25 saw a penguin update, as well as July 18 – just a few days ago.

That July 18 Panda update actually looks like it may be a turning point but it’s probably too early to call.