Which of the following describes an attempt to guess a password by using a combination of letters and numbers?

The correct answer is brute-force, which describes a method of attempting to guess a password by systematically trying every possible combination of characters until the correct one is found. This technique often employs automated tools that can test large volumes of combinations rapidly, making it effective against poorly constructed passwords or those that are relatively short.

This method not only utilizes letters and numbers but can also include special characters, fundamentally relying on the sheer computational power available to change the combinations quickly. As a result, it can be a time-consuming process, especially if the password is complex, but it does not assume any knowledge about the password other than its length and character set.

Other techniques mentioned, such as social engineering, involve manipulating individuals into divulging information rather than attempting to guess passwords directly. Dictionary attacks are a specific type of brute-force method where a pre-defined list of common words, phrases, or passwords is used, rather than purely testing every possible combination. Zero-day refers to a type of vulnerability that has not been publicly known and exploited by attackers, which is unrelated to password guessing techniques.