Any program built to work against you — stealing what you type, locking your files, or using your machine for someone else. It nearly always arrives as something you opened.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
poison hidden in the pantry.
For example
You open an attachment from what looked like a delivery company. Nothing seems to happen. Something is now running that you did not choose.
This is one card out of 275.
The hundred words you meet most are free — the whole set, animated, in one file that works with no internet.
Volume 1 has all 275 in fifteen chapters, with Staying Safe the largest chapter on purpose.