A government agency's confidential Information is leaked to the public, causing significant embarrassment and damage...

In the scenario where a government agency's confidential information is leaked, the most likely threat actor group involved would be state-sponsored hackers:

Motivation:

National Interests: State-sponsored hackers are typically employed by governments to pursue national interests, which often include espionage, stealing sensitive information, and undermining the operations of other states.

Capabilities:

Advanced Techniques: These groups possess advanced capabilities and resources, making them highly effective in penetrating secure systems and exfiltrating valuable data.

Examples:

Historical Incidents: Numerous incidents, such as the attacks attributed to APT groups like APT28 (Fancy Bear) and APT29 (Cozy Bear), have been linked to state-sponsored actors targeting government and military organizations.

References:

FireEye APT Groups: FireEye Threat Intelligence

Mandiant M-Trends Report: Mandiant