synonyms: worm, Trojan Horse
spyware (spy·ware, ˈspīwer/)
malware (mal·ware, ˈmalwer/)
What can I do to protect myself against unwanted software?
Think of your computer like a garden with lots of things trying to attack it. You need insecticide to protect it from bugs, herbicide to protect it from weeds, and a fence to protect it from animals like deer or rodents. Just like a garden, a computer has to be protected against all kinds of different threats that can come from anywhere.
Why didn't my antivirus protect me?
People often ask how they could possibly have gotten a virus when they have antivirus installed, and the simple answer is that no single antivirus can protect your computer from every threat. Every piece of antivirus software has a different strategy for identifying malicious or unwanted software and removing it from your computer without damaging your system. It takes time for the companies that produce these kinds of software to develop the best strategy to identify and remove viruses, and new viruses are developed every day.
Where do viruses and spyware come from?
People make viruses and find ways to distribute them so that you don't even notice. They do it for all kind of reasons. Some of them are just nerds without girlfriends that are looking for a way to spend their time. Some of them are criminals that are trying to exploit unsuspecting users for money or conduct fraudulent activities. In some cases, it might be governments carrying out secret operations. Whatever the reason, it ends up being like a competitive sport, and last year's defense might not be effective against this year's offense.