Ars Technica reported last year that in 2015 over two thirds of patent lawsuits were filed by trolls and that of all patent lawsuits, 44% were filed in the Eastern District of Texas (where few others than trolls would be filing suits). The report says that although the numbers are up, the trolls' business might be down.

Ars: https://arstechnica.com/tech-policy/2016/01/despite-law-chan...

Original statistic: https://www.unifiedpatents.com/news/2016/5/30/2015-patent-di...