To NSAYou are typing into a document on your PC or into a box on a website etc. You look down at the keyboard, or out of the window at the sheep. When you look back at the screen the text you had written has not appeared. And it’s not in any other window you have open. Where did the text go?
A virus can log all keystrokes on your computer. You've got a 25% chance of having a virus, based on what I know about your OS and user habits (i.e. nothing).