DjVu

DjVu was developed at AT&T Research by Yan LeCun et al. in 1966. It generates files that are smaller than PDF files. […] PDF primarily encodes graphics and text as vectorized data, whereas DjVu primarily encodes them as pixmap images.

DjVu is a relatively old and no longer developed file format devised by AT&T, used to store scanned images. None of the VirusTotal anti-virus scanners detected the CySource researchers' Base64 encoded payload added to the metadata of the malicious DjVu file. The researchers found that "instead of exiftool detecting the metadata of the file it executes our payload."

Because of Wikimedia's educational mission, MediaWiki supports file types that may be uncommon in other web applications or CMSes, like SVG vector images, and multipage PDFs and DjVus. They are rendered as PNG files, and can be thumbnailed and displayed inline, as are more common image files like GIFs, JPGs and PNGs.