surely I should use the DNS for my router. I don't really want to change it for the iMac as I access secure sites with it to internet shop.
I don't understand exactly what you are saying here nor what difference your choice of DNS services would related to the use of secure sites?
Are you saying you are using the default DNS provided by your ISP to the router? That may or may not be a good choice for speed and accuracy. There are also some security advantages of using a service such as OpenDNS or Google's public DNS.
No information (secure or otherwise) is passed to a DNS server. All it does is send back the IP address of every URL requested by your computer.
Adding Open DNS codes to your Network Preferences, should give good results in terms of speed-up as well as added security, (including anti-phishing and redirects) (Full information about Open DNS is here: http://www.opendns.com/home/nobloat ) and further independent information can be read here:
Open System Preferences/Network. Double click on your connection type, or select it in the drop-down menu, and in the box marked 'DNS Servers' add the following two numbers:
(You can also enter them if you click on Advanced and then DNS)
Sometimes reversing the order of the DNS numbers can be beneficial in cases where there is a long delay before web pages start to load, and then suddenly load at normal speed:
There are hackers that have managed to poison dns poorly secured servers.
I use Google.
BDAqua suggests in a post.
You can use OpenDNS for looking up web addresses.
Put these numbers in Network>TCP/IP>DNS Servers for a try...
I think they now pretend you need to join to use, but you don't.
(Please note that you do not need to a joint Open DNS to use it.)
Google provides free dns lookup too. There numbers are:
Thank you. Using a google DNS, 126.96.36.199 seems to have solved the problem. I was using the DNS from my router, I don't understand whether this was correct or not, it was just the way it automatically set up. I am afraid that I am no expert, however the three answers above collectively solved the problem. Excellent, thank you.