Has your Internet speed suddenly become unusually slow? Have you asked your Internet provider to test your connection, but found no connection issues? One of the apps, on one of your devices (computers, smartphones, tablets, etc.), may be consuming all of your available Internet upload or download bandwidth.
(Updates added to the bottom of article)
DSL users may find that their Internet connection seems much slower once they have upgraded a computer to Windows 10, or purchased a new computer with Windows 10. This may be due to Windows 10 downloading updates or sharing updates using what Microsoft calls Windows Update Delivery Optimization.