If you are getting notifications from WindowsMegabyte, then your Mac is infected with adware. WindowsMegabyte is adware for Mac.
WindowsMegabyte changes setting in your Mac. First, WindowsMegabyte installs a browser extension in your browser. Then, after WindowsMegabyte hijacks your browser, it modifies settings in the browser. For example, it changes the default home page, modifies search results, and displays unwanted pop-ups in your browser.