First of all, the problem has nothing to do with adware, and even if you had adware there was no need to download anything to remove it. Blithely following advice to download unknown software only puts you at greater risk of malware attack.
Back up all data before proceeding.
Triple-click anywhere in the line below on this page to select it:
~/Library/Preferences/MobileMeAccounts.plist
Right-click or control-click the highlighted line and select
Services ▹ Reveal in Finder (or just Reveal)
from the contextual menu.* A folder should open with an item selected. Move the selected item to the Trash. Log out or restart the computer and empty the Trash.
*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination command-C. In the Finder, select
Go ▹ Go to Folder...
from the menu bar and paste into the box that opens by pressing command-V. You won't see what you pasted because a line break is included. Press return.