Final answer:
A brute-force attack is when a hacker methodically tries many combinations of characters to find a decryption key, highlighting the need for robust security measures.
Step-by-step explanation:
A brute-force attack occurs when a hacker tries numerous possible character combinations to find the key that will decrypt encrypted data. Hackers use this method as a last resort when other techniques fail, as it can be time-consuming and requires significant computational power. The process involves systematically checking all possible keys until the correct one is found. This type of cyber attack underscores the importance of strong, complex passwords and encryption methods to protect sensitive information.