It is not possible to install Security Update for Windows XP (KB2686509). Anybody please suggest a solution?
Piracy talking?
Officially: Don't ever think of it.
Unofficially: Use google.
^^ there's may be lots of other reasons .
what is KB2686509 hotfix for?
This is what MS website says : A security issue has been identified that could allow an authenticated local attacker to compromise your system and gain control over it.
KB2686509 can cause installation issues the the pc has some kind of key mapping softwares installed - so OP should check if he is using any kind of apps for his keyboard.