Signs of a Compromised Network and Operating System

Detecting a compromised network and operating system is crucial for limiting potential damage and initiating an appropriate response. The following are some telltale signs that a network or operating system may have been compromised:

1. Unusual System Behavior: Unexpected changes in system behavior, such as frequent crashes, slow performance, or applications failing to start, can indicate a compromised system. These issues may arise from malware or unauthorized modifications to the system.
2. Unexplained User Account Activity: Suspicious user account activity, such as unauthorized creation, deletion, or modification of accounts, can be a sign of compromise. Additionally, unexpected password changes or locked-out accounts may suggest an attacker is attempting to gain or maintain access to the system.
3. Unusual Network Traffic: An increase in network traffic or unexpected communication with external IP addresses can indicate a compromised system. This can be a result of malware transmitting stolen data, communicating with command and control (C2) servers, or scanning the network for additional targets.
4. Unexpected Processes or Services: The presence of unfamiliar processes or services running on the system can be a sign of compromise. Malware or unauthorized tools installed by an attacker may appear as unexpected processes or services in the system's task manager or process list..
5. Security Software Disruption: If security software, such as antivirus programs or firewalls, is unexpectedly disabled, it may be an indication of a compromised system. Attackers often attempt to disable security software to evade detection and maintain persistence.
6. Unauthorized Access or Login Attempts: An increase in unauthorized login attempts, especially from unfamiliar IP addresses or during unusual hours, can suggest a compromised system. Monitoring system and application logs for failed login attempts or unexpected access patterns can help identify potential intrusions
7. File System Anomalies: Unusual file system activity, such as unexpected creation, modification, or deletion of files, can indicate a compromise. This includes the presence of unfamiliar files or directories, changes to system files, or unauthorized access to sensitive data.
8. Log Manipulation: Inconsistencies or gaps in system logs, or the presence of unexpected log entries, can be a sign of compromise. Attackers often attempt to manipulate or delete logs to cover their tracks and evade detection.
9. Unexpected Network Connections: Unexpected open ports or active connections to unfamiliar IP addresses can be a sign that the system has been compromised. Attackers may use these connections to maintain access, exfiltrate data, or perform other malicious activities.
10. Alerts from Security Tools: Warnings or alerts from security tools, such as antivirus programs, intrusion detection systems, or threat intelligence platforms, can indicate a compromised system. Investigating and validating these alerts can help determine if a breach has occurred and the extent of the compromise.

Identifying the telltale signs of a compromised network and operating system is vital for initiating a timely response and mitigating potential damage. Monitoring system behavior, user activity, network traffic, processes, logs, and security alerts can help organizations detect and address security breaches more effectively.

Perhaps one of the biggest signs that something is wrong is when the IT department notices unusual traffic patterns leaving the network.
A common misperception is that traffic inside the network is secure, says Tom Hauck, senior security strategist for DispersedNet. Look for suspicious traffic leaving the network. It is not just about what comes into your network; it is also about outbound traffic.
Considering that the chances of keeping an attacker out of a network are difficult in the face of modern attacks, outbound indicators may be easier to monitor.
The best approach is to watch for activity within the network and to look for traffic leaving your perimeter. Compromised systems will often call home to command-and-control servers, and this traffic may be visible before any real damage occurs.

The name of the game for a well-orchestrated attack is for attackers to either escalate privileges of accounts they have already compromised or to use that compromise to leapfrog into other accounts with higher privileges. Keeping tabs on unusual account behavior from privileged accounts not only watches out for insider attacks, but also account takeover. "Changes in the behavior of privileged users can indicate that the user account in question is being used by someone else to establish a beachhead in your network," Gould says. "Watching for changes such as time of activity, systems accessed, type or volume of information accessed will provide early indication of a breach."