Mainly about google algorithm and update,
Google’s Penguin Update,
Latest Algorithm, launched on April 24, target spam, so if your traffic dropped on April 24, that would be effected by Penguin update.
Panda 3.5, on April 19 - target pages that aren’t spam but aren’t great quality. The date is important. If your traffic dropped on April 19 and never recovered, then you were probably hit by Panda rather than Penguin
Parked Domains Mistake,
April 17, Around April 17, a number of sites reported lost traffic. That turned out to be a problem with how
Google was incorrectly classifying them as being parked domains. If your traffic dropped around April 17, it’s probably related to that, especially if you recovered by April 18.
Link Warnings, mid-March, Google began taking action against some blog networks that seemed chiefly designed just to generate links to those participating, in hopes of boosting rankings. Then around the end of March, Google also sent warnings about “artificial or unnatural links” to a variety of sites.
Negative SEO
Especially in the past week, there’s been a huge rise in forum discussions that “negative SEO” is now a serious problem. The idea is that if being in a blog network or having paid links could hurt you, then anyone could point bad links to harm another site.
More:
http://searchengineland.com/penguin-update-recovery-tips-advice-119650
some google update history past years:
http://searchengineland.com/14-is-google-evil-tipping-points-since-2001-10174
-cnbarry