sp.exe is a process belonging to Spy.Passkiller.
It is a key logger application running in the background and records every key entry. This process is a security risk and should be removed from your system.
Non-system processes like sp.exe originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that over time your registry suffers fragmentation and accumulates invalid entries which can affect your PC's performance. It is recommended that you check your registry to identify slowdown issues