Intrusion Detection Systems (IDS) in Cybersecurity - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary function of an Intrusion Detection System (IDS)?

Choose the best description of what an IDS does in a computer network.

A It manages user passwords and authentication credentials.

B It blocks all incoming traffic to prevent unauthorized access.

C It monitors network or system activities for malicious actions or policy violations and alerts administrators.

D It encrypts data to protect it from being intercepted during transmission.

💡 Hint

Think about what an IDS does after detecting suspicious activity.

An IDS watches network or system activity to find signs of attacks or policy breaches and then alerts the security team. It does not block traffic or encrypt data.

📋 Factual

intermediate

Which type of IDS analyzes network traffic to detect suspicious patterns?

Select the IDS type that inspects data packets traveling through the network.

A Host-based IDS (HIDS)

B Anomaly-based IDS

C Signature-based IDS

D Network-based IDS (NIDS)

💡 Hint

Consider which IDS type is placed on the network to watch traffic.

Network-based IDS (NIDS) monitors network traffic to detect suspicious patterns. Host-based IDS runs on individual devices.

🔍 Analysis

advanced

What is a key difference between signature-based and anomaly-based IDS?

Analyze the following statements and select the correct difference.

A Signature-based IDS uses machine learning; anomaly-based IDS uses fixed rules.

B Signature-based IDS detects attacks by matching known patterns; anomaly-based IDS detects deviations from normal behavior.

C Signature-based IDS can detect unknown attacks; anomaly-based IDS cannot.

D Signature-based IDS requires no updates; anomaly-based IDS requires constant signature updates.

💡 Hint

Think about how each IDS identifies threats.

Signature-based IDS looks for known attack patterns, while anomaly-based IDS identifies unusual behavior that differs from normal activity.

❓ Reasoning

advanced

Why might an IDS generate false positives, and what is a common consequence?

Choose the best explanation for why false alarms occur and their impact.

A False positives happen when normal activity is mistaken for attacks, causing unnecessary alerts and possible alert fatigue.

B False positives occur when the IDS fails to detect real attacks, leading to security breaches.

C False positives are caused by hardware failures, resulting in system crashes.

D False positives happen when the IDS blocks legitimate users, causing denial of service.

💡 Hint

Consider what happens when the IDS mistakes safe actions for threats.

False positives are alerts triggered by normal behavior mistaken as malicious, which can overwhelm security teams and reduce trust in alerts.

❓ Comparison

expert

Compare Intrusion Detection Systems (IDS) and Intrusion Prevention Systems (IPS). Which statement is true?

Select the option that correctly distinguishes IDS from IPS.

A IDS only detects and alerts on threats; IPS can detect and actively block threats in real time.

B IDS blocks malicious traffic automatically; IPS only logs suspicious activity.

C IDS requires no network placement; IPS must be installed on every host.

D IDS and IPS perform the exact same functions with no differences.

💡 Hint

Think about whether the system takes action or just reports.

IDS monitors and alerts on threats but does not block them. IPS can detect and also block or prevent attacks in real time.

Practice

1. What is the primary purpose of an Intrusion Detection System (IDS)?

easy

A. To monitor network or system activities for suspicious behavior

B. To automatically block all incoming network traffic

C. To replace firewalls in network security

D. To encrypt data during transmission

Solution

1. Step 1: Understand IDS function

   An IDS is designed to watch network or system activities to detect suspicious or malicious behavior.

2. Step 2: Differentiate from other tools

   Unlike firewalls or encryption tools, IDS does not block or encrypt but alerts about possible threats.

3. Final Answer:

   To monitor network or system activities for suspicious behavior -> Option A

4. Quick Check:

   IDS monitors and alerts [OK]

Hint: IDS alerts suspicious activity but does not block it [OK]

Common Mistakes:

• Confusing IDS with firewall that blocks traffic
• Thinking IDS encrypts data
• Assuming IDS replaces other security tools

2. Which of the following is the correct description of a Network-based IDS (NIDS)?

easy

A. Monitors network traffic for suspicious patterns

B. Monitors individual host activities only

C. Encrypts network data to prevent attacks

D. Automatically blocks detected intrusions

Solution

1. Step 1: Identify NIDS role

   NIDS monitors network traffic to detect suspicious patterns or attacks across the network.

2. Step 2: Exclude incorrect options

   It does not monitor individual hosts only, encrypt data, or block intrusions automatically.

3. Final Answer:

   Monitors network traffic for suspicious patterns -> Option A

4. Quick Check:

   NIDS watches network traffic [OK]

Hint: NIDS watches network traffic, not just one computer [OK]

Common Mistakes:

• Mixing NIDS with Host-based IDS
• Thinking NIDS blocks attacks automatically
• Confusing monitoring with encryption

3. Consider this simplified Python-like pseudocode for an IDS alert system:

alerts = []
for packet in network_traffic:
    if packet.source_ip == '192.168.1.100' and packet.port == 22:
        alerts.append('Possible SSH attack')
print(alerts)

What will be the output if two packets match the condition?

medium

A. Error: packet is undefined

B. ['Possible SSH attack']

C. []

D. ['Possible SSH attack', 'Possible SSH attack']

Solution

1. Step 1: Analyze the loop and condition

   The code checks each packet; if source IP is '192.168.1.100' and port is 22, it adds a message to alerts.

2. Step 2: Consider two matching packets

   Since two packets meet the condition, the message is appended twice, resulting in two identical alerts.

3. Final Answer:

   ['Possible SSH attack', 'Possible SSH attack'] -> Option D

4. Quick Check:

   Two matches add two alerts [OK]

Hint: Each matching packet adds one alert to the list [OK]

Common Mistakes:

• Assuming only one alert regardless of matches
• Thinking the list remains empty
• Confusing variable scope causing error

4. A system administrator wrote this IDS rule snippet:

if packet.protocol = 'TCP':
    alert('TCP packet detected')

What is the error in this code?

medium

A. No error, code is correct

B. Using single equals sign (=) instead of double equals (==) for comparison

C. Incorrect protocol name 'TCP'

D. Missing parentheses in alert function

Solution

1. Step 1: Identify the comparison operator

   The code uses '=' which is an assignment operator, not a comparison operator.

2. Step 2: Correct operator for condition

   For checking equality, '==' must be used to compare values in conditions.

3. Final Answer:

   Using single equals sign (=) instead of double equals (==) for comparison -> Option B

4. Quick Check:

   Use '==' to compare values in conditions [OK]

Hint: Use '==' for comparison, '=' is assignment [OK]

Common Mistakes:

• Confusing assignment and comparison operators
• Ignoring syntax errors from wrong operator
• Assuming protocol name is wrong

5. You want to design an IDS that detects suspicious login attempts by checking if a user fails to login 3 times in a row within 5 minutes. Which approach best applies IDS concepts to solve this?

hard

A. Use a Network-based IDS to block all login attempts after 3 failures

B. Use encryption to hide login attempts from attackers

C. Use a Host-based IDS to monitor login logs and trigger alerts on 3 failed attempts within 5 minutes

D. Use a firewall to allow only 3 login attempts per user

Solution

1. Step 1: Identify IDS type for login monitoring

   Host-based IDS monitors activities on a single computer, such as login logs, suitable for detecting failed login attempts.

2. Step 2: Understand IDS role and limits

   IDS alerts on suspicious activity but does not block actions automatically; blocking is done by other tools.

3. Final Answer:

   Use a Host-based IDS to monitor login logs and trigger alerts on 3 failed attempts within 5 minutes -> Option C

4. Quick Check:

   Host IDS monitors logs and alerts [OK]

Hint: Host IDS watches logs and alerts, does not block [OK]

Common Mistakes:

• Confusing IDS with blocking tools like firewalls
• Thinking IDS encrypts or blocks automatically
• Using network IDS for host-specific login events