What is mstask.exe

This is the task scheduler service, responsible for running tasks at a time predetermined by the user. You can use it to start services at particular times, such as running a backup overnight. This file is not essential for Windows XP. If the file exists in Windows XP, you should ensure that it is from Microsoft. This service doesn't exists in Windows Vista or Windows 7! In this case "mstask.exe" could be a virus or trojan. 

Note: The mstask.exe file is located in the folder C:WindowsSystem32. In other cases, mstask.exe is a virus, spyware, trojan or worm!