Is it possible to block Tor users?

Question

Would it be possible to block Tor users? (https://www.torproject.org/)

Due to the nature of the site I run I should do all I can to stop multiple accounts and block cert

Answer 1

Blocking Tor is wrong because (ab)users and IP addresses are not the same. By blocking Tor you will also block legitimate users and harmless restricted Tor exit nodes configured with conservative exit policies.

For example, if you concerned about attacks on SSH (port 22) then blocking only Tor will do little to increase security. What you really might need is dynamic synchronised blacklist like http://denyhosts.sourceforge.net/ that track offenders disregarding of their affiliation with Tor.

Denyhosts will automatically block Tor exit nodes that allow Tor to access port 22 without unnecessary denying access to anonymous users and operators of Tor exit nodes who never let offenders to attack your SSH services.