There is no need to download anything to solve this problem.
You downloaded and ran a malicious application that changes the settings of Safari, Chrome, and Firefox. It can have various names.
Back up all data. Open the Applications folder and press the key combination option-command-4 to arrange the contents by date added. Look at the applications that have been added since you first noticed the problem. If there is one you don't recognize, and you're quite sure it's not something you need, drag it to the Trash. If in doubt, ask first.
In Safari, open the preferences window and select the General tab. Reset the home page, or just delete the setting. Do the equivalent in Firefox, if you use that.
If you use Chrome, there is a radio button in the startup settings marked
Open a specific page or set of pages
Next to that is a hyperlink named
Set pages
Click that link and delete the pages you don't want. Save the changes.
Then select the Extensions tab in the Safari preferences window. For any extension with a name you don't recognize, select it and click Uninstall. If in doubt, delete all extensions. None required for normal operation.
If you use Firefox or Chrome, do the equivalent in those browsers.
