Hackers are exploiting an unpatched security hole in current versions of Adobe Reader and Acrobat to install malicious software when users open a booby-trapped PDF file, security experts warn. Adobe issued an advisory Thursday warning that its Reader and Acrobat software versions 9 and earlier contain a vulnerability that could allow attackers to take complete control over a system if the user were to open a poisoned PDF file. Adobe said it doesn’t plan to issue an update to plug the security hole until March 11. Meanwhile, the folks at Shadowserver.org, a volunteer-led security group, said it has seen indications that this vulnerability is being used in targeted attacks. Shadowserver warns that this exploit is likely to be bundled into attack kits that are sold to cyber crooks who specialize in seeding hacked and malicious Web sites with code that tries to install malware. “These types of attacks are frequently