Countermeasures

The effectiveness of countermeasures varies, because keyloggers use a variety of techniques to capture data and the countermeasure needs to be effective against the particular data capture technique. For example, an on-screen keyboard will be effective against hardware keyloggers, transparency will defeat some screenloggers - but not all - and an anti-spyware application that can only disable hook-based keyloggers will be ineffective against kernel-based keyloggers.
Also, keylogger software authors may be able to update the code to adapt to countermeasures that may have proven to be effective against them.