MIME Content-Type Change for Adobe Reader Updates
Adobe Reader Installers
On Windows, Adobe pushes out Adobe Reader updates as .msi (for full installers) and .msp files (for patch installers). For example, Adobe Reader 9.1, which was a full installer, was an .msi file, and Adobe Reader 9.1.3, which was a patch installer, was an .msp file.
Change in MIME Content-Type for .msi Installers
Currently, the MIME content-type for .msi files is set to text/plain. From September 19, 2009 and onwards, the MIME content-type for .msi files will be changed to application/octet-stream. According to our testing, this change will be more robust when downloading .msi through a variety of firewalls.
From an end-user perspective, there is no impact of this change in the way Adobe Reader is updated via the Adobe Updater.
Knowledge Base Article: http://go.adobe.com/kb/ts_cpsid_51355_en-us