Strange increase in visitors

I have about 100 visitors a day on my web site. Since yesterday I noticed significant increase in visitors (about 400). I checked wp_statistics_visitors database and found out that it is populated with the similar records (Firefox 40.1) but they are from different IPs and countries. I doubt that such similarity is just a coincidence and I don’t think those are real visitors. Looked at the attached Screenshot. Do you have any idea where the plugin got that stuff? I use latest version (10.3). Thank you for your help.

Screenshot

https://www.ads-software.com/plugins/wp-statistics/