What is C&C server blocking in Trojan detection?

C&C (Command and Control) server blocking in Trojan detection refers to the process of identifying and preventing communication between a compromised system (infected with a Trojan) and the attacker's remote server that issues commands or exfiltrates data. Trojans often establish covert connections to C&C servers to receive instructions, such as stealing sensitive information, deploying additional malware, or coordinating attacks. Blocking these connections is critical to mitigating the threat.

How It Works:

Detection: Security systems monitor network traffic for suspicious patterns, such as connections to known malicious IP addresses, domains, or unusual data transfers.
Blocking: Once a C&C server is identified (via threat intelligence, anomaly detection, or sandboxing), the communication is disrupted—either by firewall rules, intrusion prevention systems (IPS), or DNS filtering.

Example:

A Trojan like Zeus (a banking malware) may contact a C&C server to upload stolen credentials. If the security solution detects the Trojan's beaconing behavior (e.g., periodic HTTPS requests to a suspicious domain), it can block the connection, preventing data exfiltration.

In cloud environments, services like Tencent Cloud's Anti-DDoS Pro and Web Application Firewall (WAF) can help block malicious traffic, while Host Security provides endpoint-level Trojan detection and C&C connection prevention. Additionally, Tencent Cloud Security Center integrates threat intelligence to identify and mitigate C&C-related risks.