keylogger.exe is a versatile hacking tool which logs keystrokes silently. The most popular variant of this file, JanNet, silently logs keystrokes and automatically sends the data via e-mail to the attackers computer. In this way the attacker can retrieve personal data with the hope of maybe finding passwords.
Non-system processes like keylogger.exe originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that your registry has suffered fragmentation and accumulated invalid entries which can affect your PC's performance. It is recommended that you check your registry to identify slowdown issues