Mathcad 12 through 13.1 allows local users to bypass the security features by directly accessing or editing the XML representation of the worksheet with a text editor or other program, which allows attackers to (1) bypass password protection by replacing the password field with a hash of a known password, (2) modify timestamps to avoid detection of modifications, (3) remove locks by removing the "is-locked" attribute, and (4) view locked data, which is stored in plaintext.