Every program you run is a list of instructions your computer will follow. It doesn’t ask whether you meant to run them. Today: the main kinds of harmful software, and the defenses that actually work.
Big Idea 5 — Impact of ComputingCED 5.6 · taxonomy and defense only
Security. 7.7 tricked the person. Malware tricks the machine — usually with a person’s help.
2
The Hook
Your computer doesn’t know what you meant.
You double-click a file called free_game.exe. The computer runs every instruction in
it — including the ones you didn’t know were there. That’s it. That’s the whole problem.
3
The Idea
Malware is software designed to cause harm. Classify it by how it spreads and
what it does:
Type
How it spreads / what it does
virus
attaches to a file or program; spreads when that file is shared and run
worm
spreads by itself across networks, no clicking required
trojan
pretends to be something useful so you install it yourself
ransomware
encrypts your files and demands payment for the key
spyware
secretly collects information about what you do
keylogger
records every key you press — including passwords
Defenses, and why they work:
Software updates close known security holes that attackers are actively using. Delaying an update leaves a door open that the whole internet knows about.
Least privilege: give each account and app only the access it needs. Malware running in a limited account can only do limited damage.
Backups, kept separate from the computer, are the only real answer to ransomware: restore the files instead of paying.
Only install software from sources you trust — the answer to trojans.
The line we don’t cross. This lesson is about recognizing malware and defending
against it. We do not write, download, or test malware, and we never probe or test systems we don’t own or
have written permission to test. That isn’t just a class rule — it’s professional ethics, and in
most cases it’s the law. Unit 8 covers the legal side.
4
Try It — Name That Malware
Each scenario describes one kind of malware. Name it.
5
Vocabulary
malware Security
Software intended to damage, disrupt, or gain unauthorized access to a computer system.
virus Security
Malware that attaches to a file or program and spreads when it is run.
worm Security
Malware that copies itself across networks without needing a user to run it.
trojan Security
Malware disguised as legitimate software.
ransomware Security
Malware that encrypts a victim’s files and demands payment to restore them.
spyware Security
Malware that secretly gathers information about a user.
keylogger Security
Software or hardware that records keystrokes, often to steal passwords.
software update Security
A new version of software that often fixes security vulnerabilities.
least privilege Security
Giving users and programs only the access they need, to limit the damage if one is compromised.
6
Check
Five questions. Defenses are asked as “which would best prevent…”
0 of 5 answered
7
Impact Check
Ransomware and real people
Hospitals, school districts, and city governments have all been hit by ransomware
— delaying care, canceling classes, freezing services. The organizations that recovered fastest had
tested, separate backups. Today’s decision: check whether your own photos and schoolwork exist anywhere
besides one device.
8
Connections
Came from 7.7 — trojans usually arrive through phishing — the person installs it.
Came from 7.2 — ransomware uses real encryption against you. The key space is why you can’t brute-force your files back.
Came from 6.7 — backups are redundancy for data. Fault tolerance, again.
Next in Unit 8 — the legal and ethical frame for “we don’t do this.”