The ".aspx" file type often contains instructions for a web-based server, and these file types are often used to create dynamic Web pages. They are designed for ASP.NET, a web-based framework developed by Microsoft.
The file contains instructions for the server side of the website, which tell the browser what to do with information sent to it. Often used to make websites more interactive or customizable, ".aspx" often contains instructions that direct the content of the site to be displayed properly, such as a shopping cart or a listing of recently viewed products. If a site is coded incorrectly, it can be possible that the site sends the ".aspx" file in question instead of the actual requested file, or simply mislabels the file on the server as being an ".aspx" file. Opening an ".aspx" file unintentionally downloaded is not advised.