Every computer on the internet has an IP address. This includes web servers, as well as any other computer that you might wish to connect to. In order to make things more friendly, the DNS system allows you to refer to a computer by name rather than number, and this name is then passed to a very large lookup table in order to find out the remote machine's IP address.
That's how your web browser allows you to type in www.techsupportalert.com rather than a string of numbers.
Normally, your computer (or your router) is programmed to use the DNS server, ie the big names-to-numbers table, that belongs to your internet service provider. However, there are a handful of other companies that provide alternative DNS services which offer additional features, such as blocking access to remote machines which are known to contain malware.
One such alternative DNS service is ClearCloud, and we've written about it on these pages in the past. It's possible that you have re-programmed either your PC or your router to use ClearCloud DNS.
Unfortunately, the company behind ClearCloud DNS is shutting down the service in a few days, on 1st September. At which point, if you don't change your DNS settings to use a different DNS server, you will not be able to access any system on the internet unless you specify its IP address rather than its friendly name.
Therefore, if you are currently using the ClearCloud DNS service, it's important that you stop doing so. You can find information on how to remove the setting, and revert to your ISP's service, at http://forums.clearclouddns.com/messageview.aspx?catid=237&threadid=5146&enterthread=y
Alternatively, you can switch to a different DNS provider. Two popular services are Open DNS and Norton DNS. Better still take the suggestion from reader "Deputy" below and install the free NameBench utility from Google that will find the fastest DNS server from your location to the sites you most frequently visit.
[The two final paragraphs of this article were updated to include some excellent user suggestions]