Update at 8:45 a.m. PST: Information from security firm Symantec added.
Attackers are making the rounds and exploiting a critical security flaw in Adobe Reader 9 and Acrobat 9.
Earlier versions of the PDF-related software are also affected by the critical security flaw, which could cause the applications to crash and potentially let an attacker gain control of a person's computer, Adobe Systems warned Thursday.
Reports also surfaced that attackers have developed an exploit and are taking advantage of the flaw, the company said.
Adobe has yet to develop an update to address the vulnerability but noted it expects to have one ready for Adobe Reader 9 and Acrobat 9 by March 11. After that, the company expects to launch updates for the earlier versions of the software going back to Adobe Reader 7 and Acrobat 7.
Until then, Adobe advises, people should update their virus definitions and exercise caution when opening documents from unknown sources.
Security company McAfee noted in a blog that the current attacks appear to be targeted ones but that it expects new variants of the exploit to make the rounds as more information becomes public.
In its posting, McAfee said that malicious PDF documents began to surface at the start of the year, exploiting a vulnerability in Adobe Reader versions 8 and 9. The attackers can then take advantage of a bug in Reader to overwrite memory at gain control of executing code. After that, attackers can install a Trojan horse and from there add a proverbial backdoor to a person's computer to remotely control and monitor the infected system.
Symantec, meanwhile, reports seeing the exploit used against only a few government agencies and large corporations, and within those organizations, only a few people are targeted, said Kevin Haley, a Symantec Security Response director.
"We've seen it used in only a few small places, so it tells us it's a targeted attack and someone is not trying to use it in a widespread way," Haley said, noting fewer than 100 people have been affected since it noticed the attacks on February 12.
But he added it seems likely other attackers may try to exploit the Adobe vulnerabilities and that the range of exploits may grow beyond the malware that Symantec calls Trojan.Pidief.E.