Explained: What is 'isolated tasking' and how ISI used it for drone attack?

The probe in drone attack at Indian Air Force base in Jammu has been leading to a lot of revelations daily. As per sources, ISI may be behind the attack directly as none of the terrorist organisations have claimed responsibility until now. 

On the other hand, ISI wished to keep it top secret and hence resorted to isolated tasking. Take a look.