BREB Assistant General Manager (IT) Exam: 2021প্রশ্ন ও সমাধান

A computer virus is malicious self-replicating code that attaches itself to a host program/file. Functionally it is built from three core components:

• Infection mechanism (replicator): the code that lets the virus copy itself into other programs, files, or the boot sector, spreading each time an infected file runs.
• Trigger (activation condition / logic bomb): a condition — a date, a keystroke count, a specific event — that decides when the payload should execute (e.g., "activate on the 13th if it's a Friday").
• Payload: the actual malicious action carried out once triggered — deleting files, corrupting data, displaying a message, or opening a backdoor.

Many real viruses add a fourth, optional component:

• Concealment/stealth code: techniques (encryption, polymorphism) that hide the virus from antivirus signature scans.

stateDiagram-v2
  [*] --> Dormant
  Dormant --> Propagation: host file executed
  Propagation --> Triggering: infection spreads
  Triggering --> Execution: trigger condition met
  Execution --> [*]: payload delivered

Worked example: the classic Jerusalem virus infected .exe/.com files on execution (infection mechanism), checked the system date for Friday the 13th (trigger), and then deleted any program run that day (payload).

Exam takeaway: every virus = Infection mechanism + Trigger + Payload (concealment is a common optional add-on) — distinguishing this from a worm (self-propagating without a host file) is a frequent follow-up exam point.