Adobe Systems Inc. said Tuesday it is investigating reports that attackers are exploiting a previously unknown security hole in its Acrobat, Flash and PDF Reader applications. Adobe’s security advisory says the security weakness appears to affect Adobe Reader and Acrobat 9.1.2, as well as Adobe Flash Player 9 and 10.That’s about the extent of the information provided by Adobe at this point. Meanwhile, Symantec says it has seen several instances of this vulnerability being exploited in targeted attacks — such as those in which the attackers include a poisoned attachment in an e-mail that addresses the recipient by name. Marc Fossi, manager of development at Symantec, said the attacks the company has seen so far involve booby-trapped PDF files that take advantage of Adobe Flash functions built into Reader. Fossi said none of the attacks so far have used stand-alone Flash, such as a malicious Flash movie embedded in a