dabsoft, I expect if your module does not contain others peoples intellectual property, then you would normally own copyright. The fact that your module can be integrated with one of more computers or software systems is incidental. However, if you make your module publicly available for free via GPL or other arrangement at any time, then you would probably loose some if not all of your exclusive copyright. i.e. once in the public domain, the effect of copyright changes.
GPL implies you are granting rights for your work to be used, modified etc... though under certain terms and conditions. Some countries have international agreements on copyright. Australia and the US among some other western nations, I believe share such an agreement.
You can apply a copyright notice, but it carries little weight on its own. It all depends on the governing laws and international agreements on copyright, combined with the effect of GPL and what rights GPL grant to the public domain.
Actually you don't need to state copyright on any work, because it is implied again by any created work. However you would need to be able to prove you are the creator and owner of the work. Thus as much as it might serve as an advisory to those viewing the work, ultimately its the overriding agreements on copyright that matter the most along with the burden of proof of ownership.
Not sure about GPL, but Wiki gives you a general rundown on this. A copyright lawyer might be useful, if you need more specific detail and advice and you can also get more general copyright information from the Copyright Council. My gut feeling would be to avoid GPL if you ever intend commercialising your work.