getting HttpRequestValidationException error on .NET application with “<?php echo ”Content“…”-Collection of common programming errors

We have a .NET 4.0 application deployed on a customer’s server and while the URL for this site is technically open publicically, it is not referenced by any other site (that we know of), including search engines. However, every now and again (sometimes twice or three times in a day, sometimes once in a week), we get an exception thrown and reported;

2013-07-21 13:33:40.4226: Error>An uncaught exception occurred on the site (System.Web.HttpRequestValidationException (0x80004005): A potentially dangerous Request.Form value was detected from the client (="

Originally posted 2013-11-13 09:48:52.