In a study of its own antivirus users, Avast Software found that 60.2 percent of those with Adobe Reader were running a vulnerable version of the program, and only 40 percent of users had the newest Adobe Reader X or were fully patched.
One out of every five users also had an unpatched version of Adobe Reader that was at least two generations old, the study says.
Adobe Reader is the most popular PDF reader application and is a frequent target for malware writers. More than 80 percent of Avast users run a version of Adobe Reader.
"There is a basic assumption that people will automatically update or migrate to the newer version of any program," said Ondrej Vlcek, CTO at Avast. "At least with Adobe Reader, this assumption is wrong -- and it’s exposing users to a wide range of potential threats."
Brad Arkin, senior director of product security and privacy at Adobe, agreed with the Avast analysis. "We find that most consumers don’t bother updating a free app, such as Adobe Reader, as PDF files can be viewed in the older version," he said. "In many cases, users only update when provisioning a new machine."
Malware PDF exploit packages will typically look for a variety of security weaknesses in the targeted computer, attacking when an uncovered vulnerability is discovered. "Most exploits have been made to hit all vulnerable versions, not just one," says Vlcek. "Libraries of code are shared between various Adobe versions which also means that vulnerabilities are shared." The Avast Virus Lab did not detect a causal link between older versions of Adobe Reader and exposure to malware.
"It is actually possible to be fully patched and up-to-date if you are running Adobe Reader 8 or 9," Arkin says, "But I think a large percentage of users simply decline the update notification." Have a comment on this story? Please click "Comment" below. If you'd like to contact Dark Reading's editors directly, send us a message.