I am looking for a mechanism to prevent my software from being
pirated. My software is sold internationally.

If it is PC based :-

You might ask in the News Group: alt.comp.shareware.authors

Some will reply 'Armadillo'

You should keep in mind that any type of protection will be broken
soon after it is released. I'm not saying that you don't have the
right to protect your investment, but copy protection is a very small
barrier to people who really want to get around it and will
undoughtably annoy your ligimate customers. You will need to balance
the very real cost of the protection aganist the theoretical profit
from extra sales. Just something to think about.

There are a number of products that can be purchased to do this.  Some
are purchased and incorporated into the software during compilation. 
Some can patch an existing DLL or executable to protect it.  Most
generate trial versions and some can generate timed keys.  Some may
even be able to generate keys that are machine-specific.  They are all
cost a fair amount but if your software is really good, then their
cost will be trivial.

You can find a number of such software products by doing a search for
the keywords "software license key generation."  Peruse the sponsored
links to find many examples of this sort of software protection
product.  Be sure to get one that will incorporate properly with your
software and offers the features you need, such as trial version keys.

Let me know if you'd like some ideas about algorithms for coding your
own software protection mechanism.  If you want to focus on marketing
the software, I'd advise you simply use an off-the-shelf product
though.