Lesson 4.9.3.2

4.9.3.2 Internet security Quiz: AQA Computer Science, Unit 9

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 4.9.3.2, Internet security: 20 multiple choice questions for the AQA Computer Science (7517), Unit 9: Fundamentals of communication and networking, written with Revision Ninja.

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The 20 questions

  1. What does a packet-filtering firewall do?

    • It stores a copy of every web page requested so that users can load pages faster
    • It inspects each packet's header fields and allows or blocks it according to a set of rules
    • It translates domain names into IP addresses for the devices on the local network
    • It encrypts all outgoing traffic so that no one can read it in transit across the network

  2. What is a proxy server in the context of a firewall?

    • A server that assigns private IP addresses to devices as they join the network
    • A server that keeps a permanent record of every connection state on the router
    • A server that sits between clients and the Internet and makes requests on the clients' behalf, hiding them
    • A server that checks the header of every packet against a list of allowed MAC addresses only

  3. What does a stateful inspection firewall track?

    • The number of users who are logged in to each web server on the network at any given moment
    • The type of cable used by each device that is connected to the firewall, so that unknown cables can be blocked
    • Only the size of each packet, so that oversized packets can be blocked before they reach the network segment
    • The state of connections, so it allows return traffic only for connections that were started from inside

  4. In symmetric encryption, what is used?

    • A public key for encryption and a different private key for decryption
    • A different key for every packet sent through the network
    • The same key for both encryption and decryption
    • No key at all, relying on a hash of the message instead

  5. In asymmetric encryption, what is used?

    • A key that is never stored and is generated afresh for every message
    • Two private keys, one held by each party to the connection
    • One shared secret key that is used for both encryption and decryption
    • A public key to encrypt, and a related private key to decrypt

  6. Why is key exchange a problem for symmetric encryption?

    • Symmetric keys are too long to be transmitted across any network at all
    • Symmetric encryption cannot be used for ordinary data traffic on the Internet
    • Symmetric keys change after every packet, so they cannot be shared in advance
    • The shared key must reach both parties securely, so that an eavesdropper cannot obtain it

  7. How does asymmetric encryption help with key exchange?

    • The key is embedded in the header of each packet so that routers can read it and then decrypt the payload
    • A session key can be sent encrypted with the other party's public key, which only the owner of the private key can decrypt
    • The private key is sent openly so that the other party can decrypt the message that is sent back to the sender
    • Both parties use the same private key, so no key exchange is needed at all because the key is always known

  8. What does a digital certificate do?

    • It identifies the router that forwards each packet across the Internet, so that the route can be verified
    • It binds a public key to an identity, and is issued and signed by a trusted certificate authority
    • It stores the user's password in encrypted form on the server, so that the password can be checked on login
    • It replaces the need for encryption by checking that the data is readable by the recipient at arrival time

  9. What does a digital signature provide?

    • A copy of the message stored on a trusted server for later audit
    • Encryption of the message so that only the intended recipient can read it
    • Evidence that the message came from the holder of a private key and has not been altered
    • A list of IP addresses that have been allowed to access the message

  10. A message is signed with the sender's private key. How does the recipient verify the signature?

    • By using the sender's public key to check the signature against the message
    • By comparing the message with a copy stored in a DNS record
    • By decrypting the signature using the recipient's own private key
    • By asking the sender's firewall to confirm the message's header

  11. What is a worm?

    • A program that encrypts a user's files and demands payment for the key
    • Malware that replicates itself across networks without needing to attach to a host file
    • A device driver that is copied into the operating system during installation
    • Malware that disguises itself as legitimate software to trick the user into running it

  12. What is a trojan?

    • Software that records the user's keystrokes and sends them to the manufacturer only
    • Malware disguised as legitimate software that the user installs, giving an attacker access
    • A firewall rule that blocks all traffic from an unknown range of addresses
    • Malware that spreads by copying itself across network connections without any user action

  13. What is a virus?

    • A firewall rule that blocks packets by port number to improve security
    • A certificate that proves the identity of a website to its visitors
    • Code that attaches itself to a host program or file, and spreads when that host is run or opened
    • A separate program that runs automatically across a network without attaching to anything

  14. Which vulnerability do worms commonly exploit?

    • Strong encryption keys that are changed too often by the operating system
    • Digital certificates that are signed by a trusted certificate authority
    • Unpatched flaws in software or services that can be reached over the network
    • Packets that are routed through several routers before they arrive

  15. How can improved code quality help protect against worms, trojans and viruses?

    • Fewer bugs and vulnerabilities leave fewer weaknesses for malware to exploit
    • Better code encrypts malware so that it cannot spread across the network
    • Better code allows firewalls to be removed without any loss of security at all
    • Better code makes malware run more slowly, so that users can detect it easily

  16. Which measure protects against malware by monitoring behaviour?

    • Disabling the firewall to reduce the load placed on the processor
    • Turning off all software updates so that the existing software remains stable
    • Storing all passwords in plain text so that they can be checked quickly
    • Monitoring running processes and network activity to detect unusual behaviour

  17. A firewall allows return traffic only for connections that an internal host started. Which type of firewall is this?

    • Stateful inspection
    • Packet filtering, which checks each packet on its own
    • An asymmetric key pair used to protect each connection
    • A proxy server, which hides the client's address from the Internet

  18. A message is encrypted using the recipient's public key. Who can decrypt it?

    • Only the holder of the matching private key, which is the recipient
    • Anyone who has the recipient's public key, which is freely available to all
    • The sender, who holds the matching private key for the message
    • Any firewall on the route, because it holds all of the public keys

  19. Why is a digital certificate needed for a browser to trust a server's public key?

    • It encrypts the public key so that no one can copy it while it is in transit
    • It proves the public key belongs to the named server, as vouched for by a trusted authority
    • It replaces the need for the server to have a private key at all
    • It proves the server is fast enough to process the browser's requests quickly

  20. A firewall uses packet filtering. Which attack is least likely to be stopped by packet filtering alone?

    • Attempts to connect to a private port that the firewall is configured to block, using a spoofed address
    • A malicious payload hidden inside an allowed application protocol that exploits a flaw in the application
    • A flood of packets from an IP address range that is blocked by the firewall rules, arriving on allowed ports
    • Connections to a port that has no service and is closed to all traffic, which the firewall would refuse

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