Attackers are exploiting an unpatched bug in Adobe's popular Flash Player, according to security researchers from both Symantec and the SAN Institute's Internet Storm Centre.
"Adobe Flash Player is prone to an unspecified remote code-execution vulnerability," Symantec said in a warning posted to its SecurityFocus site. "An attacker may exploit this issue to execute arbitrary code in the context of the affected application. Failed exploit attempts will likely result in denial-of-service conditions.
"Symantec has observed that this issue is being actively exploited in the wild," the company added.
The last serious Flash vulnerability fixed by Adobe was patched last month. That bug was used in late March by a hacker to take down a laptop running Windows Vista and claim a $5,000 prize in a contest sponsored by 3Com's TippingPoint security company.
According to Symantec, Flash Player 184.108.40.206 - the version currently available for download from the Adobe site - is vulnerable to attack. Flash is used by a huge number of websites, including YouTube, to display multimedia content.
Adobe officials were not immediately available for comment.