According to the Sophos antivirus site:

Troj/Ptsnoop is a backdoor Trojan. It copies itself to \windows\system\ptsnoop.exe and changes win.ini adding 'c:\windows\system\ptsnoop.exe' to 'load = '.
You'll only have to:
1- stop the virus in memory. Do ctrl+alt+del, select it, and put the "end task" (or something like that, I use French version) button.
2- delete the "ptsnoop.exe" file in your system.
3- remove the line added by the virus in your Win.ini file.
4- reboot to verify and think to update your virus definition.

Voil*.