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CryptoLocker creeps lure victims with fake Adobe, Microsoft activation codes

Can also worm its way in through removable drives, spam attacks

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Miscreants have brewed up a variant of the infamous CryptoLocker ransomware that uses worm-like features to spread across removable drives.

The recently discovered CRILOCK-A variant can spread more easily than previous forms of CryptoLocker. The latest nasty is also notable because it comes under previously unseen guises - such as fake Adobe Photoshop and Microsoft Office software activators that have been seeded on P2P sites, a security blog post from Trend Micro warns.

Analysis of the malware, detected as WORM_CRILOCK.A, shows that this malware can spread via removable drives. This update is considered significant because this routine was unheard of in other CRILOCK variants. The addition of propagation routines means that the malware can easily spread, unlike other known CRILOCK variants.

Aside from its propagation technique, the new malware bears numerous differences from known CryptoLocker variants. Rather than relying on a downloader malware — often UPATRE — to infect systems, this malware pretends to be an activator for various software such as Adobe Photoshop and Microsoft Office in peer-to-peer (P2P) file sharing sites. Uploading the malware in P2P sites allows bad guys to easily infect systems without the need to create (and send) spammed messages.

CryptoLocker, the Bitcoin demanding ransomware menace, has infected as many as a quarter of a million machines since it first surfaced last September, according to research from Dell SecureWorks’ Counter Threat Unit.

Earlier versions of CryptoLocker typically arrived in email as an executable file disguised as a PDF, packed into a .zip attachment. A spam run targeting millions of UK consumers prompted a warning from the UK National Crime Agency back in November. Only Windows machines can be infected by the malware.

If it successfully executes, CryptoLocker encrypts the contents of a hard drive and any connected LAN drives before demanding payment of up to 2 Bitcoins (payable within 72 hours) for a private key needed to decrypt the data. The malware uses a well-designed combination of 256-bit AES and 2048-bit RSA crypto that mean that without backups victims have little choice but to pay up if they ever want to see their data again.

It's unclear whether the latest worm-like variant is a copycat or the work of the regional CryptoLocker crew. The latest variant uses hardcoded command and control nodes and omits the use of domain generation algorithm (DGA) routines to create multiple potential command points, a more sophisticated feature common in earlier variants.

"Hardcoding the URLs makes it easier to detect and block the related malicious URLs," explain Trend Micro researchers Mark Manahan and Jimelle Monteser. "DGA, on the other hand, may allow cybercriminals to evade detection as it uses a large number of potential domains. This could mean that the malware is still in the process of being refined and improved upon. Thus, we can expect latter variants to have the DGA capability."

Trend Micro's blog entry, Defending Against CryptoLocker, outlines various ways of protecting a computer and a network against CryptoLocker malware. ®

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