Anonymous instant messages
 

How can someone send anonymous instant messages

Disable IP Windows Messenger
 

I think you are getting IP messaging spam, you can stop this by disabling your Windows Messenger

To disable your Windows Messenger (in Windows XP) follow the steps below
Start -> Settings -> Control Panel
Double click -> Administrative Tools
Double click -> Services
Right-click on Messenger
Select -> Properties
Change "Startup Type" to "Disabled" and click "OK"