The issue of this happening every so often concerns me also, but, you did not state what happens afterwards, as an example, you did not post that you ran an antivirus program to correct it , but, instead , you left impression that it corrected itself. So, as richc46 has suggested , your worst case scenario would be you have been attacked by a rogue of some sort and it has changed your settings, in which case, Malwarebytes' Antimalware would detect it, if that is the only thing involved, sometimes these rogues will need other programs to stop the process first , such as Rkill , which can be found at Bleeping Computer, which is a site i participate in also.
