If your computer's configured DNS servers are changing to another set of values automatically, one of these scenarios is likely to be occurring.
To check your current DNS settings. To do so, please visit our DNS settings guide for computers and view if a DNS server is set statically with an IP address. If not (and is set to "Obtain DNS server address automatically"), please do not continue this guide as this article is not relevant. The computer configuration guide is located at https://support.opendns.com/forums/21618384.
Your DNS server settings are being changed to:
1) 127.0.0.1:
You are using DNSCrypt or the Roaming Client, and this behavior is completely expected. Please see the article at https://support.opendns.com/entries/37266750 for more information.
Solutions: There is not a problem in this case, as this is expected behavior.
2) 75.75.75.75 and/or 75.75.76.76:
You are using Comcast's Constant Guard. This security suite is provided for free by Comcast for all customers, and includes a utility that covers its users by ensuring that you are using Comcast's DNS servers.
This segment is targeted at Comcast Constant Guard users; however, it may also apply to other security suites that also automatically change DNS settings.
If you configured your router or computer for OpenDNS but notice that it isn't working, please begin by clearing your DNS cache (http://www.opendns.com/support/article/67). Next, please visit http://welcome.opendns.com and confirm if you see the check mark. If not, this may be as a result of ConstantGuard.
Solutions:
1. Open Comcast Constant Guard, and click on "Options:"
2. Set the "Set DNS Lock Protection to: to "OFF"
3. Set your DNS servers back to OpenDNS or "Obtain DNS server address automatically" using the instructions at https://support.opendns.com/forums/21618384.
Visually, please watch the following video for an example of what Constant Guard behavior would look like and how to resolve it.
https://www.youtube.com/watch?v=oZfWBA0Xa0Y
3) 209.222.18.222 and 209.222.18.218:
You are currently using a privateinternetaccess VPN service. This service's VPN client automatically sets your DNS servers to 209.222.18.222 and 209.222.18.218 and cannot be changed while you are connected to the VPN. Unfortunately, there is no way around this, and you will be unable to use OpenDNS while connected to this type of VPN client.
Solutions: Cease using privateinternetaccess for VPN service and switch providers to one that supports a standard VPN client if you wish to use OpenDNS over the VPN.
4) Avast! Internet Security 2015
If you are using Avast! Internet Security 2015, refer to our Avast! instructions page to disable their "Secure DNS" setting which may have automatically been enabled during an upgrade or install. OpenDNS also provides secure DNS as well as filtering, and disabling Avast's version will not decrease your network security.