New Locky ransomware version can operate in offline mode

The program will start encrypting files even if it can't connect to a command-and-control server

The creators of the widespread Locky ransomware have added a fallback mechanism in the latest version of their program for situations where the malware can't reach their command-and-control servers.

Security researchers from antivirus vendor Avira have found a new Locky variant that starts encrypting files even when it cannot request a unique encryption key from the attacker's servers because the computer is offline or a firewall blocks the communication.

Calling home to a server is important for ransomware programs that use public key cryptography. In fact, if they're unable to report back to a server after they infect a new computer, most such programs don't start encrypting files.

That's because the encryption routine relies on unique public-private key pairs that are generated by the attackers' servers for each computer.

First, the ransomware program generates a symmetric encryption key and uses an algorithm like AES (Advanced Encryption Standard) to encrypt files. Then, it reaches out to a command-and-control server and asks the server to generate an RSA key pair for the newly infected computer.

The public key is sent back to the ransomware program and is used to encrypt the AES encryption key. The private key, which is required to decrypt what the public key encrypted, never leaves the attackers' server and is the key that users get when they pay the ransom.

Because of this process, some ransomware infections can be rendered ineffective if a network firewall detects their connection attempt and blocks it as suspicious right from the start.

Companies can also quickly cut off a computer from the Internet if a ransomware detection is triggered to try to limit the damage. They can also take the whole network offline temporarily until they can investigate if other computers have also been affected.

These measures are no longer viable for Locky, one of the most widespread ransomware threats plaguing users today, because of the changes made to it.

The good news is that Locky will start encrypting files using a predefined public key that's the same for all offline victims. This means that if someone pays the ransom and obtains the private key, that key will work for all other offline victims as well.

Security researchers from F-Secure have observed two massive spam campaigns distributing Locky this week, one of them reaching 120,000 spam hits per hour, more than 200 times higher than the spam hits on a regular day, the researchers said in a blog post.

Both campaigns spread emails with rogue zip attachments that contained malicious JavaScript files. The use of JavaScript files to distribute malware has become an attacker favorite in recent months. Such files can be executed on Windows out of the box, without any special software.

Join the PC World newsletter!

Error: Please check your email address.

Our Back to Business guide highlights the best products for you to boost your productivity at home, on the road, at the office, or in the classroom.

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Lucian Constantin

IDG News Service
Show Comments

Essentials

Lexar® JumpDrive® S57 USB 3.0 flash drive

Learn more >

Microsoft L5V-00027 Sculpt Ergonomic Keyboard Desktop

Learn more >

Mobile

Lexar® JumpDrive® S45 USB 3.0 flash drive 

Learn more >

Exec

Audio-Technica ATH-ANC70 Noise Cancelling Headphones

Learn more >

Lexar® JumpDrive® C20c USB Type-C flash drive 

Learn more >

HD Pan/Tilt Wi-Fi Camera with Night Vision NC450

Learn more >

Lexar® Professional 1800x microSDHC™/microSDXC™ UHS-II cards 

Learn more >

Budget

Back To Business Guide

Click for more ›

Most Popular Reviews

Latest News Articles

Resources

PCW Evaluation Team

Azadeh Williams

HP OfficeJet Pro 8730

A smarter way to print for busy small business owners, combining speedy printing with scanning and copying, making it easier to produce high quality documents and images at a touch of a button.

Andrew Grant

HP OfficeJet Pro 8730

I've had a multifunction printer in the office going on 10 years now. It was a neat bit of kit back in the day -- print, copy, scan, fax -- when printing over WiFi felt a bit like magic. It’s seen better days though and an upgrade’s well overdue. This HP OfficeJet Pro 8730 looks like it ticks all the same boxes: print, copy, scan, and fax. (Really? Does anyone fax anything any more? I guess it's good to know the facility’s there, just in case.) Printing over WiFi is more-or- less standard these days.

Ed Dawson

HP OfficeJet Pro 8730

As a freelance writer who is always on the go, I like my technology to be both efficient and effective so I can do my job well. The HP OfficeJet Pro 8730 Inkjet Printer ticks all the boxes in terms of form factor, performance and user interface.

Michael Hargreaves

Windows 10 for Business / Dell XPS 13

I’d happily recommend this touchscreen laptop and Windows 10 as a great way to get serious work done at a desk or on the road.

Aysha Strobbe

Windows 10 / HP Spectre x360

Ultimately, I think the Windows 10 environment is excellent for me as it caters for so many different uses. The inclusion of the Xbox app is also great for when you need some downtime too!

Mark Escubio

Windows 10 / Lenovo Yoga 910

For me, the Xbox Play Anywhere is a great new feature as it allows you to play your current Xbox games with higher resolutions and better graphics without forking out extra cash for another copy. Although available titles are still scarce, but I’m sure it will grow in time.

Featured Content

Latest Jobs

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?