Cannot delete virus infected file

Try pest patrol. As far as the news I gathered, this twain-tec act as a real browser like your IE, so firewall let this in. The best removal is the pest patrol, it can detect and eliminate twain-tec. Another is this info from a site awhile back.
If you want to uninstall, you can do so easily through the add/remove function in your control panel. You can access your control panel by going to:
1. Start (typically, the button in the bottom left of your screen)
2. Choose SETTINGS
3. Choose CONTROL PANEL
4. Choose ADD/REMOVE PROGRAMS
5. Select twain-tech
6. Click on ADD/REMOVE
In the absence of an entry in ADD/REMOVE PROGRAMS please use on of the following methods:

For Windows98 and WindowsXP users:

a) To permanently disable the software click "Start" and then "Run" and type the following command which unregisters the software: regsvr32 c:\windows\twaintec.dll "
b) To completely remove the software: reboot and then Find and Delete the file mxtarget.dll. For Windows2000, WindowsME and WindowsNT users:
a) To permanently disable the software click "Start" and then "Run" and type the following command which unregisters the software: "regsvr32 c:\winnt\twaintec.dll "
b) To completely remove the software: reboot and then Find and Delete the file twaintec.dll.