network policies

None, if you didn't have them sign an acceptable use policy. When a user is issued an account, they should sign a policy stating what is acceptable and what is not. This is your receipt and your course for legal action when they violate it.
Other than breaking state and/or federal laws for child pornography or file sharing copyright software or music, you must specifically tell them what the purpose of your network is for and define what is acceptable behavior.

good luck,
0bytes

Howdy,

In a natural law way, the business tools are owned by the employer, so they're to use for gettin' on with the job, for the term of employment and on tehe condition that you give your best effort . . . .