[AC Question]

and how do I stop it from keep coming back?

[Rukbat]

It's a text file (plain printable characters) of some sort. Exactly what it is can only be determined by opening it in a text file reader and seeing what's in it. How you stop it from downloading depends on what you see in it. (If it's from an attorney telling you that you're being sued, you'll want to take action. If it's from Hillary Clinton telling you to vote for her, you might want to take another kind of action.)