We work in an organisation which is supposed to be HIPAA compliant. Security is a big concern for us. We've been tasked to find out if any user is using anonymous proxy in the network.

Is there a way we can find if Tor is being used inside our corporate network domain? We're using Symantec client protection. VPN is provided using Cisco.

You can use a list of Tor (uplink) nodes, add this to the outgoing firewall, setup a task to update this once a day and you'll be good. But Tor can also be used over a HTTP(S) proxy, so you will have to detect proxies as well.

I am not sure if this is going to help you secure anything. As long as there is a connection to the internet, it would be possible to bypass these kind of security measures. You could end up spending endless time and energy to prohibit all kinds of proxies, VPN's, SSL tunnels and such. The advice is to just make sure they cannot do any harm by protecting whats important to your business, and leave users be. For example separate the network in compartments, use subnets, VLANs, DMZs and require authentication and authorization on private networks. Keep the important stuff in one zone, while allowing networking without restrictions on another. And so on...
