One Wrong Character

This reading describes three kinds of data in which a single changed character makes the information incorrect. Each example is presented once in its correct form and once with exactly one character changed.

A Bank Record and a Password

A bank record stores an account balance as a number, written to the cent. Suppose the correct record reads 1,250.00 dollars and one digit is changed, so the record reads 7,250.00 dollars. The record now reports 6,000 additional dollars that the account does not actually contain. NIST describes data integrity as the property that data has not been changed, destroyed or lost by accident or without permission. A bank record with one changed digit has lost its integrity.

A password follows the same principle. NIST guidelines require an authentication system to verify the entire password a person enters, without cutting off any part of it. If an account's password is Lake7river and a person types Lake8river, one character is different, and the sign-in fails.

A Line of HTML

The third example is a line of HTML from Picking Fruits, a student game built in September for the class arcade. The correct line is `<h1>Picking Fruits</h1>`, which makes the game's title a heading. In the changed line, the slash in the closing tag is missing, so it reads `<h1>Picking Fruits<h1>`. Without the slash, the browser interprets the second tag as the beginning of a new heading instead of the end of the first one.

The HTML standard tells the browser exactly what to do next. First, the browser closes the first heading. Then it opens a second heading, and every element after it on the page is placed inside that second heading. When both versions were tested on a plain page in the Chrome browser, the broken page still loaded and displayed no error message. However, the game's instruction "Tap the screen to start" appeared in large bold heading type instead of ordinary paragraph text.

Sources: NIST, Data integrity (n.d.); NIST, SP 800-63B-4 (2025); WHATWG, HTML Parsing (2026); Muggivan, HTML test (2026).