The exploit affects Microsoft Windows 98, ME, NT, 2000, XP, and Server 2003, according to Trend Micro.
"Based on our findings, the shell code (that was heap-sprayed) jumps to another shell code inside the PDF file" before extracting and executing the backdoor, Trend Micro said. The backdoor "is also embedded in the PDF file and not the usual file downloaded from the Web."
Variants of the Protux backdoor typically provide an attacker unrestricted user-level access to a compromised machine and previously exploited vulnerabilities in Microsoft Office files, according to Trend Micro.
Adobe announced on Thursday that it would release an update to fix the hole on Tuesday, the same day as Microsoft's Patch Tuesday.