Basically, if you control the entry and exit nodes of a user, you can correlate their traffic. So, if a group had control of large numbers of servers, eventuall

Basically, if you control the entry and exit nodes of a user, you can correlate their traffic. So, if a group had control of large numbers of servers, eventually (faster or slower depending on what proportion of tor servers they controll) they would be able to view a targeted user's traffic.