This might be because there is some malicious process disguises itself as the legit executable file.
So, this file is not the one that causes any problems, although some users noticed an unusual high CPU usage by this process. It runs on the system background and can be located in the \Windows\System32 folder. Rundll32.exe is a legitimate executable file for various DLL or Dynamic Link libraries – vital files that store parts of data that belongs to a particular application.
