If the computer does not belong to you then you are to do exactly what the owner says to do with it! No matter what you think or may find out - it is the fact that security is in place and rules are made to be followed.
We just this last month fired 3 more employees for failing to use their company computers correctly. All 3 had gotten a virus and it was due to personal use of IM and personal emails. My company has a zero tolerance for improper use of computers. Proper and improper use is set out in a guideline which you have to read and sign that you completely understand you are agreeing to it. Otherwise you will be terminated immediately upon any type of failure to do so by any means.
It is sad company's have to do such things to ensure their security on the net. But I've looked at what has happened to people in the past. Which did not follow those rules and they caused all kinds of very bad problems for security. Thus I must agree with what those guidelines say and follow them to the letter.
If your company needs you to use such a messaging application then they will install a network type of messaging program. But would it not be easier to use a phone? Or for that matter an intercom?
Company emails are sent via share point server where I work and it is the best way to get any good message to anyone anywhere. Due to the fact that a lot of the people I email via this system has a blackberry phone and will get the email asap!!!
Good luck and be careful there - you could get a virus or pickup something on your computer and loose your job because of it.
It is not worth it~!!!
SGT