Which of the following storage types is MOST vulnerable to magnetic damage?

HDD (Hard Disk Drive) is a type of storage device that uses magnetic disks to store data. HDD is the most vulnerable to magnetic damage among the options given because magnetic fields can interfere with the read/write heads or the magnetic disks, causing data loss or corruption. Flash, SSD (Solid State Drive), and Optical are not types of storage devices that use magnetic disks to store data. Flash and SSD are types of storage devices that use flash memory chips to store data. Optical is a type of storage device that uses laser beams to read or write data on optical discs, such as CDs, DVDs, or Blu-ray discs. References: CompTIA IT Fundamentals+ Study Guide: Exam FC0-U61, Second Edition, Chapter 3: Computing Components, page 122.