Answer: C) Whaling
Explanation:
Whaling is defined as the hacking act in which hacker tends to search and hunt for confidential and high security data for attack and then using it for their own purpose.Those malicious practice is usually done on powerful and reputed position, organization such as banks, CEO's office etc.
According to the question,whaling is taking place in the office of CEO through attacking his confidential resources to gain access and use it for further attack and benefits of his own.He has left no remaining logs of exploitation in sort amount of time.
Other options are incorrect because pivoting,key-logging and malicious linking does not include hunting information and attacking.Thus, the correct option is option(C).