The problem is likely not on your computer. The DNS checker uses your IP address to perform a lookup of "thinkbroadband.com". If there is a successful response containing the IP address, it means there is a DNS server running somewhere, allowing requests on the WAN interface on the router, and so anyone can connect. It is normal for a DNS forwarding server to be running on the router, but it should only be available to devices on the LAN interfaces, eg ethernet ports or wifi.
What is the model of the modem/router you are using? You either need to perform a software upgrade if one is available to fix this issue, or add firewall rules on the router to close incoming requests on port 53 to the outside world. If neither of these is possible, I advise you call your ISP and inform them of the problem, assuming your modem/router is provided by them.
However, if you are using a standard home connection, it is unlikely that you will receive probes or requests on port 53. There is only real cause for concern if the DNS server running has a significant vulnerability or is part of a malware package running somewhere on the network. This is unlikely because the malware would need to log in to the router and open port 53.
Edited by haggismn (Sun 15-Jul-12 13:35:54)
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