Researchers on Monday clashed over whether recent attacks that exploit a bug in Adobe Reader are the work of the group that hacked Google and dozens of other major corporations late last year.On one side, Mountain View, Calif.-based antivirus giant Symantec, whose security analysts said they've found evidence suggesting that the group which wormed its way into Google's corporate network in December 2009 is back in business.On the other, Atlanta's much smaller SecureWorks, where researcher Don Jackson said that Symantec had "comingled" evidence of two separate attacks.At issue were recent PDF-based exploits attached to messages touting renowned golf swing coach David Leadbetter that have exploited an unpatched bug in Adobe's popular Reader PDF viewer.