This one could be installed via that download trojan. Not everything will be caught by antivirus programs. So if there is a new trojan out there, Norton should recognize it and release an update for it.
Your log is clean. If you disabled System Restore, make sure to enable it now.
To help prevent future spyware installations/infections, please read the Anti-Spyware Tutorial (
http://www.greyknight17.com/spyware.htm#prevent) and use the tools provided.
Are there any problems now? If not, you should be set to go.