Still using Windows XP? Unplug it and back away from the computer. It is now highly vulnerable and no longer gets updated by Microsoft. If you don’t keep your computer’s operating system up to date, as well as all the software installed on it, you can suffer from being hacked quite easily, often through one of the other mechanisms in this list.
As annoying as it can be to install updates and reboot, it is vital to remaining safe online.