There are several words that MSN Messenger doesn't allow you to use as a display name. Most offensive words are banned, but there's a set of words (mostly business-related) that aren't offensive (unless the title network administrator is offensive to you), but banned nonetheless. So far, I've found that:

are banned. That is, they can not be in any part of your display name. So what does this mean? Is MS afraid of users posing as Bob from Accounting, a sysadmin, or a message? Using l33t sp34k or some ãltérn@te lé+te®s is an easy workaround if you really need to use one of these words, but why disallow them in the first place? Some of them (administrator, Microsoft, etc.) do have some potential for trouble. For example:

MSN Administrator says:
We're having server problems and we need your password, or you will be banned from the system.

However, some of them puzzle me. What would you do it you saw:

Network says:
This is your network speaking. I need your password!


Your email says:
Hey, I forgot your password, could you tell me one more time, so I can retrieve your mail?

Apparently, it's just Microsoft covering all the bases it can, protecting the extremely gullible. But, as aozilla has pointed out, it can be quite irksome if your real name contains one of these "banned" words.