Spammers have made several attempts to modernize the technology used in creating spam emails (image spam) during the first six months of 2007. The share of spam with graphical attachments (.gif,.jpeg, etc) began to decrease. In January, the share of graphical spam amounted to 33% of all spam, but in March numbers were down to 25.7%. The decline continued with graphical spam registering a mere 18.8% in June. Spam in PDF and FDF attachments will not open automatically, nor will it be downloaded automatically.”]
Source: https://securelist.com/spam-evolution-january-june-2007/36173/