IBM ISS X-Force say they re seeing infected PDFs being spammed out and that it looks like the traffic is mainly coming from Taiwan, though those may be spoofed addresses. JBIG2 exploit-laden PDFs are now being sent alongside other PDF exploits through spam bots, seemingly originating from Taiwan. This one is especially tricky with certain email clients since components that exploit Adobe are sometimes rendered in advance by simply opening the email (and not the attachment) As with many of these file format vulnerabilities, portions of the file are auto-loaded by many applications.
Source: https://threatpost.com/ibm-iss-adobe-jbig2-exploits-being-spammed-out-031709/72414/