Okay Firstly you should have anti virus on at all times unless you know that what ever your downloading has false positives (:
Basicly The most common type of keylogger you will get is when you download a program that is like runescape gold generator.
Here is what it will do
You will download it.
You will boot it.
The program will disapear. Or will it ?
So in order to stop it thieving all your password you need to boot up task manager, click on the process tab, make sure its listed by name and find the name of the program and click end task. job done delete the file from your pc completly and you will be safe.
End of story. Best thing you can do is not be an idiot and think that you can hack runescape in any way at all. ITS SERVER SIDED PEOPLE..... but have fun botting ^.^
p.s this was intended for other games not just runscape.