gouri - 1:28 am on Jan 2, 2013 (gmt 0)
Only your raw logs will help establish the possibility of it not being human visitors. What sort of spike are you talking?
I apologize for not writing sooner. I had not looked at this thread for a couple of weeks.
I believe that the spike that I saw occurred during a one-hour interval on one day and after that, I have not seen something similar to this.
Another thing that I should mention is that the impressions to different pages of the site during this interval are around the same.
Does this help to figure out what it could be?