A Simple Definition
Malware is short for malicious software — any program written with harmful intent. That single category covers a surprisingly diverse menagerie, each with different goals, propagation methods, and defences.
Viruses
A virus attaches itself to a legitimate program or document. When the host file runs, the virus runs too — and tries to attach itself to other files on the system.
- Spreads by: user executing the infected host.
- Classic example: macro viruses in Word documents.
- Detection: trivial for any modern scanner if the signature is known.
Worms
A worm is self-propagating. It does not need a host program — it spreads by exploiting network vulnerabilities directly.
- Spreads by: scanning the network for vulnerable systems and exploiting them.
- Classic example: WannaCry (2017), Conficker (2008).
- Why dangerous: can infect thousands of machines in minutes with no user action.
Trojans
A trojan disguises itself as a legitimate program. Unlike viruses, trojans do not self-replicate — they rely entirely on the user installing them.
- Spreads by: social engineering, fake downloads, cracked software.
- Classic example: a fake "video codec installer".
- Common goal: open a backdoor for the attacker.
Ransomware
Ransomware encrypts the victim's files and demands payment for the decryption key. Modern strains also exfiltrate data and threaten public release if the ransom is unpaid.
- Spreads by: phishing emails, RDP brute force, unpatched VPN appliances.
- Recovery: restore from clean offline backups; do not pay.
Spyware
Spyware quietly observes user activity — keystrokes, browsing, screenshots — and sends it back to the attacker. Stalkerware is a particularly invasive subtype.
Adware and PUPs
Adware displays unwanted advertising. PUPs (Potentially Unwanted Programs) include browser hijackers, search-engine redirectors, and aggressive notification poppers. Not strictly malicious, but disruptive and usually deceptive.
How They Get In
Despite the variety, almost every infection enters via one of just five vectors:
- Email attachments that the user opens.
- Malicious links that lead to drive-by downloads.
- Cracked or pirated software.
- Unpatched vulnerabilities in internet-facing services.
- Infected USB drives plugged into the system.
Close those five doors and you have already eliminated most opportunistic attacks.
What You Can Do Today
- Enable automatic OS and browser updates.
- Use a reputable antivirus and keep it running in the background.
- Scan unknown files before opening — that is exactly what Virus Purge is for.
- Treat unexpected email attachments as suspicious until proven otherwise.
- Back up important data to a drive that is not always connected.
A little caution beats a lot of clean-up.