A new zero-day exploit targeting Adobe Reader, as well as 9.1.3 and earlier versions of Adobe Systems' Acrobat, drops a backdoor onto computers using JavaScript, Trend Micro researchers warned on Friday.

Trend Micro identified the exploit as a Trojan horse dubbed "Troj_Pidief.Uo" in a blog post. It arrives as a PDF file containing JavaScript-based malware, "Js_Agent.Dt," and then drops a backdoor called "Bkdr_Protux.Bd."

The exploit affects Microsoft Windows 98, ME, NT, 2000, XP, and Serv...