Virus

Description

It travels on USB sticks, mail attachments, shared folders and pirated software. Through the nineties and the early two-thousands it was the dominant form of malware; today it has been pushed aside, because attackers prefer quiet threats that bring money to noisy ones that only cause damage. It has not disappeared entirely.

In everyday speech the word virus has become a synonym for all malicious software, although it names only one kind. A virus, like the real thing, is passed on by close contact — from application to application. A Trojan, a worm, ransomware and an infostealer work by entirely different rules, and defending against them looks different.

Examples

• ILOVEYOU (2000) spread as a mail attachment — a love letter. The moment the victim opened it, it forwarded itself to every contact in the address book while overwriting files on the machine along the way. Within a few days it caused damage measured in millions of dollars.
• CIH (Chernobyl) erased the BIOS on infected machines, leaving them unable to run at all.
• An infected macro in a shared Office document moves from file to file across a company network, multiplying each time somebody opens an infected document.

Notes

• A virus needs a host and a human.
• When somebody says they have detected a virus, they usually mean any malicious threat at all. The defense depends on which threat it actually is.