Unfortunately i think you will find that taking action against them would be pointless as the file they are offering for download is not your program. It is just a file that tells the torrent client where to look to find copies of your file on individual users PC's where it is then downloaded from.

The only way would be to download a torrent client and download your program from the network and monitor the download for all IP addresses sharing the file, you would then need to take action against all the individuals sharing the file, which in the long run will probably cost you more than you would make through legitimate sales to all the illegal down loaders.

As mentioned previously, you would be better releasing a Shareware with nag or restrictions, you will be more likely to get people to pay to get the unlock code.