About a month from now Microsoft will be cutting off older versions of Internet Explorer, meaning these installs will no longer receive new security updates. To prevent security risks, you should install an alternative browser or ensure you run IE9 on Windows Vista, IE 10 on Windows Server 2012 and IE11 on Windows 7 and 8.1.
Unfortunately, a lot of corporations face the same problem as with Windows XP, they run custom software that depends on legacy software and can't upgrade to a newer version of Microsoft's browser. The Register learned that there's at least one big corporate client that signed up for an expensive Custom Support Agreement (CSA) to continue to receive security updates. The site didn't learn the name of the firm, but heard it's a very large manufacturer running almost 100,000 desktop PCs with a combination of Windows 8.1 and Internet Explorer 8.
A Microsoft spokesperson told The Register about the new CSAs: “We will continue to provide technical support and security updates for the most current version of Internet Explorer available for supported versions of Windows. If customers have a technical or business issue that prevents upgrading, we encourage them to reach out to their Microsoft account team or Microsoft partner.”
In case of Windows XP, these CSAs were very expensive as the software giant didn't want to be stuck permanently supporting legacy software. Pricing was $200 per desktop for year one, $400 for year two and $800 for a third year. Unfortunately, some firms migrated to IE8 on Windows 8.x because it provided the path of least resistance, and are now stuck with the same issue.