A write blocker is a hardware device or software tool used in cybersecurity and digital forensics to prevent any data from being written or modified on a storage device, such as a hard drive or USB stick, while still allowing read access. This ensures that investigators can safely examine and copy data without risking alteration or contamination of the original evidence. Write blockers are essential for maintaining the integrity of digital evidence during forensic analysis, as even minor changes can compromise the validity of the investigation or legal proceedings. There are both hardware and software write blockers, but hardware versions are generally preferred for their reliability.