Connection problem may be caused by a virus
If you are unable to connect to the internet or some websites, you might be affected by malware that changes the DNS settings on your computer. Even if your anti-virus tells you your computer is clean, you might still be affected. In Jul 2012 there was a major threat from a bug called DNS Changer that spread globally. The Australian government even set up a website, now not functional, to check for that specific bug.
How to test DNS
To check your computer for DNS issues today visit dnsleaktest dot com. The reported DNS servers should correspond to your provider or public DNS Servers set up by your IT, such as Google DNS or Open DNS.
DNS server is translating a human-readable web address to an IP address which is numbers. In a sense, the DNS server is equivalent to a mail sorting post office. DNS servers can track websites you visit, hence it is tempting for rogues to scope data or divert you to the websites they want. Usually, DNS is managed by your ISP provider, if you are at home or the IT department in an organisation.
If your DNS servers do not belong to the expected company you should contact IT support or at least do a thorough computer antivirus scan.
30 March 12, updated 2021