Drops every Sunday¹. Employees of companies are using Tor to bypass company site blocks.
¹ https://metrics.torproject.org/users.html?graph=userstats-re...
¹ https://metrics.torproject.org/users.html?graph=userstats-re...
https://metrics.torproject.org/users.html?graph=userstats-re...
There was a huge spike in Mid 2013, cause by a botnet that installed tor. Before there was almost not oscillation. After that there is quite a bit. I think there are many infected PCs at companies.