i keep receiving prompts from messenger service warning me of virus in my computer. Is there any cause for concern? any idea, anyone?
It is most likely spam.
Microsoft Windows NT, 2000, and XP systems allow anyone on the network to pop up messages on your screen using the "net send" command. There is no need for the sender to know anything about your computer and your computer does not care who sends it.
You could try disabling the Messenger Service, but in doing so Windows would not being able to alert you when there is a genuine problem. Refer to below article for more details:
http://support.microsoft.com/default.aspx?scid=kb;en-us;330904