Quick Answer
The answer is to isolate the host from the network. This is the best first step because containing ransomware by isolating the host immediately cuts off communication with the command-and-control (C2) server and prevents lateral movement to other systems, which stops the attack chain at the host level. On the Cisco CyberOps Associate 200-201 exam, this scenario tests your understanding of the containment phase in incident response—specifically that network isolation takes priority over deletion or analysis, as those actions could trigger encryption. A common trap is choosing to delete the file or run a scan, but the EDR agent has already flagged it, so the goal is to stop propagation, not investigate further. Remember the memory tip: "Isolate first, investigate second"—breaking the network link buys time for safe remediation.
This 200-201 practice question tests your understanding of host-based analysis. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company's endpoint detection and response (EDR) agent is reporting a file that was created with a name matching a known ransomware pattern. The analyst suspects the file is malicious. What is the best first step to contain the threat?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Create a new firewall rule
Why wrong: Firewall rules may help but isolation is more immediate and comprehensive.
Isolate the host from the network
Isolation prevents lateral movement and C2 communication.
Run a full antivirus scan
Why wrong: Scanning may take time and does not prevent network propagation.
Delete the file
Why wrong: Deleting the file does not stop running processes or network spread.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Isolate the host from the network
Isolating the host from the network is the best first step because it immediately stops the ransomware from communicating with its command-and-control (C2) server and prevents lateral movement to other systems. The EDR agent has already flagged the file as suspicious, so the priority is containment, not further analysis or deletion, which could trigger the ransomware to encrypt data. Network isolation breaks the attack chain at the host level, buying time for forensic analysis and remediation.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Create a new firewall rule
Why it's wrong here
Firewall rules may help but isolation is more immediate and comprehensive.
Isolate the host from the network
Why this is correct
Isolation prevents lateral movement and C2 communication.
Clue confirmation
The clue words "best", "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Run a full antivirus scan
Why it's wrong here
Scanning may take time and does not prevent network propagation.
Delete the file
Why it's wrong here
Deleting the file does not stop running processes or network spread.
Common exam traps
Cisco often tests the principle of 'containment before eradication' — the trap here is that candidates choose to delete the file or run a scan, thinking that removing the artifact stops the threat, but they overlook that the ransomware may already be executing in memory or have established persistence.
Detailed technical explanation
Host isolation in an EDR context typically involves applying a network access control (NAC) policy or using the EDR agent to block all inbound and outbound traffic except to the management server, often via a host-based firewall rule or by disabling the network interface. Ransomware often uses domain generation algorithms (DGAs) to resolve C2 domains, so blocking at the host level is more effective than relying on DNS or IP-based firewall rules. In a real-world scenario, a ransomware strain like Ryuk or Conti may have a built-in delay before encryption, making immediate isolation critical to prevent the encryption key from being fetched from the C2 server.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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FAQ
Host-Based Analysis — This question tests Host-Based Analysis — Read the scenario before looking for a memorised answer..
The correct answer is: Isolate the host from the network — Isolating the host from the network is the best first step because it immediately stops the ransomware from communicating with its command-and-control (C2) server and prevents lateral movement to other systems. The EDR agent has already flagged the file as suspicious, so the priority is containment, not further analysis or deletion, which could trigger the ransomware to encrypt data. Network isolation breaks the attack chain at the host level, buying time for forensic analysis and remediation.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "best", "first". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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