GCSE (9-1) Computer Science
Mark Scheme
J277/02: Unit 2.3 Defensive Design & Testing
Question Answer Marks Guidance
1ai SQL Injection 1
Do not accept "hacking" or "virus". Must be specific.
1aii Sanitisation removes/strips dangerous characters (like ; or ') (1) so the input is treated as text/string rather than a command (1). 2
Ghost Topic: Frequently confused with Validation. Validation checks if data is sensible; Sanitisation modifies it for safety.
1b Validation: Checking data is sensible/reasonable/meets criteria (1).
Verification: Checking data matches the original source / is copied correctly (1).		 2
"Checking if data is correct" gets 0 marks.
2 (a) To check the highest value that results in a Fail (1).
(b) Output "Fail" (1).
(c) 40 (1).
(d) To check that data outside the valid range (upper limit) is rejected (1).
(e) Error message displayed / Asks for input again (1). 		5
(c) 41 is NOT a boundary. (e) Do NOT accept "Crash" or "Nothing happens".
3a Line 05 (1).
Correction: elif len(pWord) < 8: (1)		 2
Missing colon : is a common syntax error.
3b Line 07 (1).
Explanation: It returns True when the password is too short / it should return False (1).		 2
Ghost Topic: Length checks on strings often trip students up more than range checks on numbers.
4 attempts = 0
auth = False
while attempts < 3 and auth == False:
  pwd = input("Enter password: ")
  if pwd == "Secret123":
    print("Access Granted")
    auth = True
  else: attempts = attempts + 1
if auth == False: print("Account Locked") 		6
1 mark each for: Init counter, Loop condition, Input inside loop, Correct IF check, Increment counter, Success handling, Failure handling.
5a 1. Indentation: Shows the structure/hierarchy of the code (2).
2. Meaningful Variable Names: Using attempts instead of x (2).
(Alternative: Subprograms/Modules). 		4
Ghost Topic: Forces recall of structural maintainability beyond just "Comments".
5b 1. Iterative Testing (1).
2. Final / Terminal Testing (1).		 2
6a Runtime Error / Execution Error 1
Do not accept "Logic Error" for division by zero crashes in J277.
6b if num2 == 0:
  print("Cannot divide by zero")
else: print(num1 / num2) 		3
1 mark for checking divisor, 1 for error message, 1 for valid division logic.
OCR 2026