To properly uninstall TrendMicro OfficeScan 10.5 and have forgotten the uninstall password, you can very easily change it to something familiar, assuming you have administrative permissions on the computer.

1. Locate and open the INI-file Ofcscan.ini. By default this is located at:
   %PROGRAMFILES%\Trend Micro\OfficeScan Client\Ofcscan.ini
   Note that on 64-bit, the default install path will probably be %PROGRAMFILES(X86)%\Trend Micro\...
2. Search for the line beginning with:
   Uninstall_Pwd=!CRYPT!364EB2
3. Although the password is encrypted in a hash, you can quite easily replace the hash with another hash of a password you do know. You can use this MD5 hash generator for it.
4. In the configuration file, remove everything after Uninstall_Pwd=!CRYPT!, and add 111 followed by your password hash. E.g. if you want to change the password to password, change the line to:
   Uninstall_Pwd=!CRYPT!1115f4dcc3b5aa765d61d8327deb882cf99
5. Save the file, then perform the uninstall through Control Panel.