System DNS and the protection service

To filter every program on your PC, AdBolish points your network adapters' DNS at itself (127.0.0.1). Here's how that works and how you get your settings back.

The protection service

Changing an adapter's DNS servers is a system setting that Windows only lets an administrator make. So AdBolish installs a small Windows service, AdBolish Protection Service, with your permission once (at install, or when you click Set up). The service does the system-wide part: it answers your PC's DNS from the moment Windows starts, for every account on the PC, and the AdBolish app talks to it. The app itself never asks for administrator rights.

Because the service filters the whole PC, what it blocks is shared by everyone who uses it: your blocklist choices, exclusions, custom blocks and statistics live with the service in %ProgramData%\AdBolish, a folder only administrators can open.

Without the service, AdBolish still runs its filter at 127.0.0.1, but only lookups sent there directly are filtered (test with nslookup doubleclick.net 127.0.0.1), and the banner System-wide filtering isn't set up offers Set up.

Settings ▸ Protection ▸ Protection service shows Running · v… (or Not set up with Set up). The service updates itself when AdBolish updates, without asking; if an update of the service fails, this row says why.

Turning routing on and off

In Settings ▸ Protection, Route this PC's DNS through AdBolish switches routing (it needs the protection service). When it's on, the hint names the adapters being routed. The header banner's Route system DNS button does the same when routing is off.

New networks are picked up as you join them; AdBolish tells you with a note like Now also filtering Wi-Fi 2. Names on your VPN keep resolving through the VPN's own DNS (shown as VPN: rows under Resolver in Settings).

How your DNS is restored

Your original DNS settings come back whenever AdBolish stops routing:

• when you turn Route this PC's DNS through AdBolish off;
• when the protection service stops, including when Windows shuts down;
• when you uninstall AdBolish (the uninstaller removes the service, which restores them first);
• if the service ever crashes: Windows restarts it within seconds, and it repairs your settings as it starts.

Quitting the AdBolish app doesn't change your DNS: the service keeps answering, so your internet keeps working.

If your internet stops working

AdBolish watches itself. If lookups keep failing, it stops routing your DNS so your network's DNS takes over and nothing stays broken. You'll get a notification (AdBolish paused system-wide filtering) and a banner, System-wide filtering is paused because DNS lookups kept failing. It resumes on its own once lookups work again.

What usually goes wrong

• The switch is greyed out. The protection service isn't set up. Click Set up.
• "Could not switch system DNS: …" Windows refused the change, often because another app (a VPN client or another filter) controls the adapter. Close that app and toggle routing again.