My thumbdrive has been hit by some trojan virus and is a threat to other computers. However, when i used Norton Antivirus to scan the files in it, it shows no signs of virus. This can't be possible whichever computer which the thumbdrive had been used on gave series of warnings even before i open the files in it. Is there a way where i can track the virus in it manually without using any antivirus programme? Why isn't Norton antivirus responding to such obvious threats? I understand that an antivirus programme cant completely detect all viruses but to totally miss them is a serious issue. What could possibly be the reasons behind?