Adware keeps installing itself
It is possible for adware, as well as other "viruses" to be installed on the sd card. Thus even doing a factory reset can reinstall the "virus". If you have access to a pc with virus protection on it. You can mount the phone as a USB storage and scan it from there. Besides wiping both the phone and the sd card. There may not be a permanent fix. But if you are able to locate the file and delete it from there. That may fix it.