Denied Access, even though im administrator, UAC NOT ENABLED

Backstory: I think some of you experienced this problem, Square ads are popping up in my firefox's bottom corners, after some searching, people say this is done with the "hosts" file

I tried to use Hijackthis to get a better idea of whats going on with my computer, and when i run it, it confirmed my suspicion, my system denied me access to the Hosts file and its the same even when i run it as administrator, I checked UAC but its already at the lowest level

Also i noticed there are strange "CREATOR OWNER" and "Trusted installer" groups when i try to change the ownership and permission, however no matter how i try it just keep saying "Access is denied" and i cant change anything

Help pls

Help pls this is really scary idk if i got a trojan or some backdoor in my computer

Instead of trying to mess with the permissions of the HOST file, should have just moved it to your desktop then modify it there. After putting it back to its original location.

Hosts File : Use in Windows 7 / Vista

install and update Malwarebytes ,MBAM, then run it while your computer is in safe mode. Works almost everytime.

Also disabling UAC isn't recommended, a lot of viruses can get through that way.