How to stop an unstoppable windows 7 service?

Many security software installs a special driver that intercepts any changes to its services and processes.

However, the driver is normally not loaded in Safe Mode, so you can disable the service there. If the service is still started after reboot, you may want to find and disable the driver in Device Manager. This kind of driver is normally under the "Non-plug and play drivers" section which is viewable by selecting "Show hidden devices" from the View menu. The name of the driver is normally well-known for each provider.

What about opening regedit.exe and go to

HKLM\SYSTEM\CurrentControlSet\services\[service name]

Than change the service to disable (I think you can do that by changing the "Start" value to 4).

The valid service Start types are:

• SERVICE_BOOT_START (0): A device driver started by the system loader. This value is valid only for driver services.
• SERVICE_SYSTEM_START (1): A device driver started by the IoInitSystem function. This value is valid only for driver services.
• SERVICE_AUTO_START (2): A service started automatically by the service control manager during system startup. For more information, see Automatically Starting Services.
• SERVICE_DEMAND_START (3): A service started by the service control manager when a process calls the StartService function. For more information, see Starting Services on Demand.
• SERVICE_DISABLED (4): A service that cannot be started. Attempts to start the service result in the error code ERROR_SERVICE_DISABLED.

Use taskkill command followed by the service's process ID. This will kill the service.