What internet security are you talking about?
And posting your serial number is not going to be helpful, especially if you want someone to steal your authentication and use it to register their software. Never post that type of information on a public forum.
Also, read your Terms of Use, maybe your only allowed to use it on 2 computers at a time without buying a new license. Or, maybe they changed their Terms of Use and reduced the amount of computers a license can be used on. Companies to that a lot. I would contact the Software manufacturer, they should have a phone number included in the literature that comes with the software.