Ransomware is making a comeback, plaguing users with extortion demands of up to $120 to return documents or drives to their control, security experts said today.
There appear to be two different campaigns underway, said Chet Wisniewski, a senior security adviser at antivirus vendor Sophos.
"It looks like we're looking at different samples," said Wisniewski, referring to analyses done by Sophos and other security firms, including Kaspersky Lab and CA.
Last week, Sophos came across malware that used malicious PDF documents to exploit one or more since-patched vulnerabilities in Adobe Reader. If successful, the malware sniffed out a wide range of file formats -- including numerous media formats, Microsoft Office and OpenOffice.org document formats and image formats -- then partially encrypted those files to make then unreadable.
To unlock the encryption, the scammers demanded $120, and for good measure threatened users.
"Remember: Don't try to tell someone about this message if you want to get your files back!" an on-screen warning stated. "Just do all we told."
Wisniewski said that as of today, there was no way to decrypt the modified files, although Sophos' researchers were working on a solution. "It's not likely you're going to be able to brute force it," he said, talking about the 1024-bit encryption key that locks the files. "We'll look at how it's generating the keys, and if that's predictable, we may be able to offer some kind of tool that creates the key."
Other security companies have reported seeing the same ransomware, the term used to describe a scheme where hackers plant malware that encrypts files and then displays a message demanding money to unlock the data.
On Monday, Russian antivirus vendor Kaspersky Lab said that it, like Sophos, had analyzed the new ransomware , which it claimed was a stronger version of a long-running bad apple dubbed "GpCode."
Unlike the previous variants, it doesn't delete files after encryption," wrote Kaspersky researcher Vitaly Kamluk on the company's blog. "Instead, it overwrites data in the files, which makes it impossible to use data-recovery software such as PhotoRec, which we suggested during the last attack."
As Kamluk noted, GpCode has a long history, first surfacing six years ago and then reappearing in 2008.
Many of the GpCode variants have been "mostly hot air," Kamluk said.
In 2007, a GpCode Trojan said it had locked encrypted files with a 4096-bit key, a claim Kaspersky later revealed as bogus . The company has had success coming up with tools to help infected users reclaim their files.
U.S.-based CA reported Tuesday on a different kind of ransomware that tried to infect the master boot record, or MBR, of the hard drives of Windows machines, crippling them and making them unbootable.
Instead, an extortion note appears on the screen. "Your PC is blocked," the message reads. "Any attempt to restore the drive using other way will lead to inevitable data loss!!!:
The extortionists demand $100 for an unlocking key.
Because the MBR has been replaced, claims that the drive has been encrypted are just part of the hoax, CA said. "Rescue disks and boot disks can be used to restore the MBR of the infected system," the company said on its blog.
Kaspersky had a simpler solution . "Use the password 'aaaaaaciip' (without quotes) to restore the original MBR," advised Kaspersky researcher Denis Maslennikov in another entry on the research lab's blog.
"There's a resurgence of using this tactic," said Wisniewski of Sophos. "We've not seen any successful ransomware for quite some time, but the appearance of two in such a short time is probably not a coincidence."
Users running the newest version of Adobe's Reader, which that company released two weeks ago, are safe from the PDF-borne malware, said Wisniewski. Reader X includes a "sandbox" designed to protect users from PDF attacks; Wisniewski confirmed that the sandbox stops the rogue PDF from infecting a Windows PC.
"And this is a great reason to do regular backups," Wisniewski added.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer or subscribe to Gregg's RSS feed . His e-mail address is firstname.lastname@example.org .
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