ctfmon.exe is a Microsoft process which runs in a background when you run a Microsoft Office XP or Microsoft Office 2003 programs. This file controlls Alternative User Input and the Office Language bar but it can also be seen running even when you close all Microsoft Office programs. Ctfmon.exe process is only necessary when dealing with other languages or when information in inputted using a device other than a standard keyboard, so it's not an essential process. If you don't need it, you can safely terminate it. Typically, ctfmon.exe can be found in subfolder "C:\WINDOWS\System32\" when running Windows XP.
ctfmon.exe file can sometimes be used by malware to hide its presense on the system, so pay attention to the location of the file. If it is located not in C:\WINDOWS\System32, these is a huge possibility that this file belongs to virus, spyware, trojan or worm. Note that ctfmon.exe is mostly used by parasites Satiloler, Satiloler.d, Satiloler.c, Satiloler.e and Snow, so you are highly advised to scan the system, delete executable ctfmon.exe and terminate all the processes it started.
Do NOT mix ctfmon.exe with ctfmon32.exe file because this file is related to such parasites as the CoolWebSearch hijacker, Raidys and Family Key Logger. The primary purpose of this file is to start a parasite or launch some of its components. Once executed, the ctfmon32.exe file runs a process that is responsible for the parasite's payload. ctfmon32.exe is a significant part of a dangerous threat, but it can also work on its own. DO NOT execute it!
If you suspect that ctfmon.exe is malicious and causing various problems on your computer, you should not only terminate this process but run a full system scan with SpyHunter or other problems listed below to find and eliminate errors related to ctfmon.exe
Information added: 2012-11-26 04:59
Information updated: 2013-12-30 00:22