MODEM ON THE DESK EARNS A PINK SLIP AT SUN
Citing users with dial-up Internet access as the No. 2 biggest security risk
after internal hacking, Sun Microsystems has made it a firing offense to
have a modem on the desk.  Many crackers use a technique called "war
dialing" in which their computer tries hundreds or even thousands of phone
numbers in search of an idle modem.  If that PC's owner is not using the
machine, the cracker can effectively "capture" the PC, and gain access to
the network it's connected to.  If a senior manager at Sun discovers an
infraction, that employee is "gone the same day," says one of Sun's security
managers.  "Any dial-up line is a tremendous risk."  (Network Week 18 Mar
98)

[Just because a user doesn't actively use the computer does NOT
 make it automatically vulnerable. The user must be running some kind of 
 software that allows dialin access, and control over the machine in the
 first place.]