A password is a string of characters proving you own the account. If it is weak, the whole account is.

First: make it long, because longer ones are harder to crack.

Second: mix upper and lower case letters, digits and symbols (A, b, 1, @).

Never use personal details (birth date, phone number), and never reuse it on other services.

You forgot your password and tapped "recover". A message arrives with a 6-digit code.

That is an OTP: a password used only once that keeps changing.

It arrives on your phone as an SMS or in your email.

After you use it, it expires. Even if it leaks it is useless, which blocks unauthorized access.

When you log in, the system must be sure it is you. That process is authentication.

Knowledge-based: something you know (password, PIN). Biometric: something about your body (fingerprint, iris).

Possession-based: something you have (smart card, OTP). Two-factor: two different factors, like a PIN then an SMS.

And two-step: two steps of the same kind, like a password plus a secret question.

At school the teacher can enter grades. The student? He cannot change them.

That is access control: a method that protects systems and data.

It lets only authorized people in and use the information, and blocks everyone else.

It relies on authentication to confirm who is trying to get in.

The school network is connected to the internet. How do we stop a suspicious visitor from getting in?

A firewall is a security system placed where the network meets the internet; it watches data coming in and out.

It allows safe connections and blocks suspicious ones.

Its jobs: stop intruders and viruses, keep data from leaking out, and monitor traffic.

Four simple steps protect your device and data from viruses and harmful programs.

Install antivirus software that finds and removes or isolates them, and update its definitions because viruses evolve.

Update the operating system and apps, because updates close the security holes attackers exploit.

And make regular backups on an external drive or cloud storage.

A password of only 3 characters, with digits and lowercase letters. How many combinations exist?

Digits 0 to 9 give 10, letters a to z give 26. That is 36 choices for each position.

So the number of combinations = 36 × 36 × 36 = 46,656.

Every extra character multiplies that, making a brute-force attack much harder.