As you many IE8 users noticed recently there was an error with SmartScreen Filter that caused many legitimate sites to be reported as phishing/malware websites. Normally SmartScreen Filter acts as a passive protection that can help you avoid known websites that are designed to steal information, or install viruses and unwanted software.

SmartScreen Filter is automatically included in Internet Explorer and can be disabled through the options menu.

Smartscreen Filter works by checking websites against a Microsoft database of known malware sites, which then tells your browser whether or not the website has known issues. Unfortunately on November 5, a server error at Microsoft caused SmartScreen Filter to malfunction by reporting a large portion of websites as unsafe. This included many ASP.NET and Silverlight sites, as well as those using third-party controls, such as Telerik. Microsoft has not gone into details on the cause of the problem, but from our vantage point this appears to be a case of not enough testing before a production deployment.

Fortunately the problem only lasted a few hours, and the Microsoft team was able to resolve the issue. However, the outage still caused a lot of confusion and created many problems.

First, it rendered many legitimate websites unusable for IE8 users. These included websites built on some of the most popular technologies, and impacted a large amount of web-based companies. Also, approximately one-third of internet users (31%, as of September 28, 2010) use IE8 to browse the web.

This can have a large impact on ecommerce sites whose users are already skeptical of online safety and generally easily frightened by security risks. Imagine how you may feel if Microsoft displays a bright red security warning when you visit your favorite ecommerce site. It could cause consumers to question that company and makes users less likely to return to complete future purchases.

We become aware of the problem early on and were able to quickly assign senior technical staff to diagnose the issue and determine which client systems were impacted, while simultaneously working with Microsoft and others to resolve the issue. As a custom software company, we have helped build many websites and web applications for our clients and we continue to watch and monitor issues such as these to ensure that current and past clients are aware of issues that can impact their ability to conduct business.

For more information on this issue, we invite you to ask questions in the comments. Special thanks to of our customers (Dave, you know who you are) who helped us diagnose the problem.