Which activity involves the unauthorized modification of data?

Data tampering specifically refers to the unauthorized alteration or manipulation of data. This can involve changing, deleting, or falsifying information within a database, file, or data transmission, with the intent to deceive or mislead. This activity poses severe risks to the integrity and reliability of information, which can be especially critical in contexts such as finance, healthcare, or national security.

While the other options involve security breaches, they do not focus on the unauthorized modification of data. USB device misuse pertains to the improper use of portable storage devices, account masquerading involves impersonating another user to gain unauthorized access, and unauthorized downloads relate to acquiring files without permission. Each of these has its own implications for security, but none directly describe the act of changing data, which is the core of data tampering.