Keylogger's are softwares which records every keystroke in a PC that you are working in. It has a normal visible mode and stealth mode. If it s installed in stealth mode you cannot see it. It can also be made hidden in Add/Remove progs. Likewise many hacking softwares, keyloggers and keygens will be caught by the Anti-virus Progs. So its better to disable the AV while installing those stufffs. But be sure that the software you are installing does'nt contain any harmful virus. If u hav any doubts about keyloggers rep?