Bangladesh Bank Assistant Programmer Exam: 2019 (DU)প্রশ্ন ও সমাধান

Protecting a computer from malware requires layered defence (defence-in-depth); no single control is sufficient.

Preventive measures

• Install reputable antivirus/anti-malware with real-time scanning and keep signatures updated.
• Keep the OS, browser, and applications patched — most malware exploits known, unpatched vulnerabilities.
• Enable a firewall (host + network) to block unsolicited inbound connections.
• Least privilege — do daily work from a standard (non-admin) account.
• Install software only from trusted sources; verify digital signatures/checksums.
• Email/web hygiene — never open unknown attachments or click suspicious links (phishing is the top infection vector); use spam filters.
• Disable autorun/autoplay for removable media to block USB worms.

Detective/responsive measures

• Schedule automatic scans and monitor logs/alerts.
• Keep regular offline backups so ransomware cannot hold data hostage.
• Use application whitelisting and browser sandboxing where possible.
• In organizations: network segmentation and an IDS/IPS.

If infected: isolate the machine (disconnect network), run a full scan/removal in Safe Mode, restore from a clean backup if needed, and change passwords afterward.

Exam takeaway: malware protection = patch + antivirus + firewall + least privilege + backups + user awareness — technology alone cannot substitute for safe user behaviour.

A firewall is a network security device/software that monitors and controls incoming and outgoing traffic based on a defined set of security rules, forming a barrier between a trusted internal network and an untrusted external network (the Internet).

How it works:

• Inspects each packet's header (source/destination IP, port, protocol) — packet filtering.
• Modern firewalls track connection state (stateful inspection), allowing only return traffic that matches an established session.
• Rules form an ACL: traffic matching an "allow" rule passes; everything else is dropped by default ("default-deny").
• Can also perform NAT, VPN termination, and application-layer inspection (proxy/next-gen firewalls).

Placement in a LAN: the firewall sits at the network perimeter, between the Internet-facing router/modem and the internal LAN switch, so every packet entering or leaving the LAN must pass through it.

graph LR
  I((Internet)) --- R[Border Router]
  R --- F[["Firewall"]]
  F --- SW[LAN Switch]
  SW --- PC1[Workstation 1]
  SW --- PC2[Workstation 2]
  SW --- SRV[(File/DB Server)]

Exam takeaway: a firewall is a perimeter gatekeeper placed between the router and the internal switch/LAN, enforcing allow/deny rules on all traffic entering or leaving.