200-201 Security Monitoring Practice Question
An analyst receives a YARA rule that includes the string 'MZ' at the beginning of a file. What does this indicator typically help identify?
⚠ Common exam trap
Cisco often tests the concept of file magic numbers to see if candidates confuse the 'MZ' signature of Windows executables with other common file headers, such as '%PDF' for PDFs or 'PK' for ZIP archives, leading them to select a plausible but incorrect option like malicious documents or PDFs.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Windows executable files
The string 'MZ' (0x4D 0x5A) is the magic number for the MS-DOS header, which is present at the very beginning of all Windows Portable Executable (PE) files, including .exe, .dll, and .sys files. A YARA rule that checks for 'MZ' at offset 0 is specifically targeting the PE file format, which is the standard executable format for Windows. This indicator helps an analyst quickly identify that a file is likely a Windows executable, regardless of its extension.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Windows executable files
Why this is correct
The ASCII bytes 'MZ' (0x4D5A) form the DOS header signature at offset zero of every Windows PE file, so a YARA rule matching 'MZ' at the start of a file identifies Windows executables. This satisfies the scenario's need to flag executable files by their magic number.
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PDF files with embedded JavaScript
Why it's wrong here
The 'MZ' magic bytes mark Windows PE executables, not PDFs, which begin with '%PDF'. Embedded JavaScript appears inside PDF objects, so a YARA rule targeting it would match those structures. This option would be correct if the rule were written to detect script-laden PDFs rather than the DOS header signature.
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Linux ELF binaries
Why it's wrong here
Linux ELF binaries start with the magic bytes 0x7F followed by 'ELF', so a rule anchored on 'MZ' cannot match them. The option tempts because YARA is commonly used to classify executable formats. It would be correct if the rule specified the ELF header instead of the DOS MZ signature.
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Malicious documents containing macros
Why it's wrong here
Macro-bearing documents are OLE or OOXML containers, whose headers are D0 CF 11 E0 or 'PK', not 'MZ'. The option tempts because malicious macros are a frequent YARA target. It would be the right choice if the rule matched VBA project streams or the compound file header rather than the PE signature.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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