I was mildly impressed with this LifeHacker article which defined malware terms. The descriptions are reasonably accurate. I didn’t start shouting at my laptop about how horribly misguided its authors were, which is usually what I deem to be a good article in the mainstream-ish press. Considering how frequently even malware experts disagree, it seems a reasonable benchmark.
I’d like to amend and clarify a couple of points, after reading the comments. I’m sure this will cause a couple people to shout at their computer due to my oversimplification, but I’m not trying to address every last corner-case.
Malware can be broken down into two basic categories, viruses and trojans.
Malware itself simply means “code created with malicious intent”.
Viruses are self-replicating code. That means code which copies itself.
Trojans are malicious code which is not what it purports to be.
Worms are viruses which copy themselves over networks (email, IM, web, whatever)
There are viruses and trojans for every major operating system, and for most minor ones.
There is more malware written for Windows machines, this does not mean other OSes are immune or not-targeted.
Most drive-by-downloads and “browser hijacks” are trojans. Most rootkits are trojans. Same with scareware, spyware, ransomware and backdoors.
Adware is not strictly speaking malware but a “security concern” or Potentially Unwanted Program as its presence/functions are often poorly documented and many system administrators consider its presence on their network undesirable.
Most malware these days is not intentionally data-destructive. That’s not to say it isn’t unintentionally data-destructive. Regular incremental backups are a good safety precaution – malware these days tends to wriggle its way so deeply into systems that many people recommend to just nuke and pave a compromised machine.
Does this clear things up?