a.exe is registered as the W32.Ahlem.A@mm worm which is transmitted via e-mail and attempts to install itself on your computer.
This process is a security risk and should be removed from your system. Please see additional details regarding this process.
Non-system processes like a.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