It seems that the Sudden drop in indexed pages reported in  WMT might relate  to some reporting issues from Google - https://productforums.google.com/forum/#!topic/webmasters/qkvudy6VqnM;context-place=topicsearchin/webmasters/sitemap|sort:date

Since "teracent-feed-processing" didn't followed the rules in robots.txt,  we had to hard-block it. If server detects the user agent beeing "teracent-feed-processing" it  will drop the connection: _ (104) Connection reset by peer_

It seems that "teracent-feed-processing" user agent is somehow linked to Google. If you analyse the Ip's , you'll noticed that are Google owned. Teracent company has been bought by Google in 2009.

btw - we've already blocked it,  but I'm trying to figure it out what's the key role played by this user agent. We've also noticed a drastic decline in number of pages being reported in Google Webmaster Tools (half of what we used to have).  Should I  assume that the drop in reported indexed pages is a result of blocking the teracent-feed-processing user agent?

Does anyone knows some info about  "teracent-feed-processing" user agent?

IP's from which user agent reside:  74.125.113.145, 74.125.113.148, 74.125.187.84 ....

In our logs, 2 out of 3 requests are made by it,   causing server crash.

Since "teracent-feed-processing" didn't followed the rules in robots.txt,  we had to hard-block it. If server detects the user agent beeing "teracent-feed-processing" it  will drop the connection: _ (104) Connection reset by peer_