The Instant Messenger MSN Messenger prevents a user from starting multiple instances of the application. Running multiple instances might be useful for users who want to use different accounts for business and private contacts or two separate businesses.
It would be possible to use two different clients, for example MSN Messenger and Meebo to connect with two different user IDs but that would mean to cope with two different applications. A more straightforward way is offered by the MSN Messenger tool Polygamy (via Technobuzz) which patches MSN Messenger so that it can be run in multiple instances.
The software is able to patch various versions of MSN Messenger and Windows Live Messenger including the latest official releases and several beta versions of the Instant Messenger clients.

The MSN Messenger patch comes basically with two switches, one for enabling multiple logins and one to disable the feature again. All the user needs to do is to make the selection and click on the Patch button to patch the file.
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Look at http://apatch.org
also Messenger plus live has the same function along with all the other features included in it.
http://www.msgpluslive.net
Or it could be used by people who arr faking to be someone they’re not. Aint that right…