Grockster is a peer to peer file sharing system, but it is not without cost. The istallation comes with spyware, keystroke recorders and what would be seen elsewhere as trojans. Well respected site, CNET, offers this programme for download wiht the following warning:
Editor's note: This download includes additional applications bundled with the software's installer file. Third-party applications bundled with this download may record your surfing habits, deliver advertising, collect private information, or modify your system settings. Pay close attention to the end-user license agreement and installation options.
Use of the programme will, in common with all peer to peer transfer programmes, render you vulnerable to allowing malicious code into your machine or network by invitation. Caveat emptor in extremis.