Using a PDF attachment in a spam message to fool the anti-spam detection methods. Spam originated with ordinary text, which can be easily scanned. Image spam came next, making it more difficult to detect; however, spam filters learned to recognize image spam patterns. In 2007, PDF spam followed image spam as yet another attempt to circumvent the anti-spam routines. Although anti-spam detectors can be enhanced to read PDF files, it takes time to open a PDF file and scan its contents. See spam.