What does it mean that a friend sent a text message and received ZC 16?

What does it mean that a friend sent a text message and received ZC 16? This is a program verification code.

The verification code is a public automatic program, which is used to distinguish whether the user is a computer or a person. It can prevent malicious password cracking, ticket brushing and forum flooding, and effectively prevent a hacker from constantly trying to log in to a specific registered user and using a specific program to violently crack. In fact, using verification code is a popular way for many websites now, and we have realized this function in a relatively simple way. This question can be generated and judged by computers, but only humans can answer it.

Because the computer can't answer CAPTCHA's question, the user who answers the question can be considered as human.