If you are browsing the Internet and suddenly get windows popping up telling you that you are infected with a virus, do NOT install whatever software those warnings tell you to install. It’s a trap; the program is a virus, and very unfortunate things will happen to your computer if you install it. If this is your work computer, unfortunate things may happen to the entire company network, and your boss will remember that when your next employee review comes around.
As a bonus, the ‘warning’ windows are sometimes designed so that the X you click on, thinking you are closing the window, is actually part of the trap, and clicking there will install the virus. Press ALT-F4 on your keyboard to close the window instead, or CTRL-ALT-DEL, open the Task Manager, and End Task on Internet Explorer.