When Microsoft created windows 8, they took their free antivirus (previously called Microsoft Security Essentials) and built it into the operating system as Windows Defender. (If you are using Windows Vista or 7, consider dowdloading Microsoft Security Essentials)
There is now no reason to install McAfee or Norton antivirus on your computer. Often these programs slow down your computer and their processes can interfere with the running of other programs or delete their files as false positives. All antivirus companies have removal tools for their programs.
Robert O'Callahan wrote an article suggesting at all antiviruses should be disabled, which automatically starts Windows Defender on Windows PCs.
It is much better to install an anti-malware program such as MalwareBytes. The free trial will give your realtime protection for 14 days. It will help remove any infections you may currently have and prevent any from affecting you in the future.
Malwarebytes also have a one hit fix program called ADWCleaner. It cleans out all traces of malware infections including Ask.com
I tend to run ADWCleaner on all Windows computers I work on as there is a common tendancy for computer users to be unaware their computer is infected with malware.