Answer:
a. indirect
Explanation:
When a system is attacked by a hacker and this infected system is used to attack other systems then it is called indirect attack. This type of attack is often initiated by a 3rd party computer. It is difficult to find from where this kind of attacks is originated.
Direct attack is when a system is attacked directly by an attacker by installing malicious software or often by getting unauthorized physical access to a computer. So option b is not true.
So the correct option is a. indirect.
