Trojan:Win32/Alureon!inf detected and removed by Windows Malicious Sofware Removal Tool June 2009

My laptop (Vista, Office) running NIS2009 (defaults) just updated via Windows Update and on restart the "Microsoft Windows Malicious Software Removal Tool - June 2009" dialog box popped up and message said "Malicious software was detected and removed from your computer - click to view details".  I clicked and it said that "Trojan:Win32/Alureon!inf" had been detected and deleted.  Should I be worried?  Bit concerned that NIS2009 running defaults didn't pick this up.