Twitter May Be Used to Host Random Content

Fact: Twitter uses Amazon’s S3 AWS to store user images.
Fact: Twitter apparently only checks the file extension to determine the file type of uploaded images, not an image library or a method that checks for binary image data.
Fact: This can be used (or abused) to obtain un-metered free hosting of files that are less than 800K in size.

How is it done? A user can rename any file with a ‘jpg’ ‘gif’ or ‘png’ extension and upload it as their background image on a dummy Twitter account.