Which technique would a threat actor use to disguise traces of an ongoing exploit?

Which technique would a threat actor use to disguise traces of an ongoing exploit?

• Create an invisible iFrame on a web page.
• Corrupt time information by attacking the NTP infrastructure.
• Encapsulate other protocols within DNS to evade security measures.
• Use SSL to encapsulate malware.

Explanation: The Network Time Protocol (NTP) uses a hierarchy of time sources to provide a consistent time clock to network infrastructure devices. Threat actors may attack the NTP infrastructure in order to corrupt time information that is used in network logs.