First of all I personally think it's wrong to use such a service, because ads are monetizing method that doesn't require the users to pay. Blocking ads decrease the profitability of this method, and hypothetically if everyone would use ad blocking service, we will have to start to pay money to visit sites.
AdFree uses the "hosts" file to redirect advertisement sites addresses back to your device, and this way blocking the communication to the advertisement site server.
AdFree have a problem when uninstalling it - it doesn't undo the changes it did to the "hosts" file.
Because of this even after uninstalling the application advertisement sites are still blocked.
In order to undo these changes you have to edit the "hosts" file.
To do this you need a rooted Android smartphone (you probably have one because it's required in order to use AdFree), and a text editor program that can edit the file.
I recommend using ES File Explorer. (Adfly link)
Setting ES File Explorer
First you need to setup ES File Explorer to be able to access root file and edit them.
To do so you need to:
1. Open ES File Explorer.
2. Press the menu button and select "Settings".
3. In the "Root settings" section check "Root Explorer" and "Mount File System".
Editing the hosts file
After you done setting ES File Explorer, you can edit the "hosts" file and remove AdFree's blocking.
1. Navigate to the hosts file and open it. The hosts file located at:
/system/etc/hosts
(Press the "up button to go to the root folder - "/")
2. Delete everything.
3. Add the line "127.0.0.1 localhost"
Optional: Add anything else you want. (if you know what you are doing)
Last step is to restart the smartphone and AdFree blockage is removed!
