Good idea. A quick and dirty solution like this would do the job for the sort term. Unfortunately too many of my users are very computer savvy, thus I have to block ICQ, Yahoo, MSN, Jabber, Meebo, and many others at the firewall.
We had at one point 100+ hours per week wasted between 10 users. 2 hours a day they were chattin with friends. This is the sort of reason my upper management wants to be very sure that there is no IM outside, or that I just shut it off entirely.
One other nice option would be to have IM internal, IM external, and IM On/Off capability.
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