Ransomware pushers up their game against small businesses

Throughout June and July, over 67 percent of users who clicked on malicious links in CryptoWall-related emails were from the SMB sector, researchers from antivirus vendor Trend Micro found. An additional 17 percent were from within large enterprises.

CryptoWall is one of the most widespread ransomware programs, infecting nearly 625,000 systems between March and August 2014 and many more since then. Researchers estimate that it has earned well over $1 million for its creators.

Trend Micro's statistics for another common ransomware program known as TorrentLocker also suggests that SMBs are increasingly being targeted.

Small and medium-sized companies accounted for over 40 percent of clicks on TorrentLocker-related URLs in June and July. The number exceeds 50 percent when large enterprises are included.

However, unlike big companies, SMBs are less likely to use sophisticated security and backup solutions that can prevent ransomware infections and help them recover encrypted files, the Trend Micro researchers said in a blog post.

Compared to consumers, SMBs are also more likely to give into this type of extortion because the files stored on their computers are often critical to their operations and also because they can afford paying the ransoms, which typically exceed $500.

Trend Micro researchers have seen many emails that were crafted specifically for business users during recent ransomware-related spam campaigns. Some of the most common lures include resumes, customer orders, passport scans, as well as notifications from postal services, telecommunications companies, utilities and government bodies.

TorrentLocker in particular is well known for its localization efforts. For example, in Turkey the ransomware gang often sends emails that masquerade as notifications from a courier service called Turkish Cargo or mobile operator Turkcell. In Italy, it impersonates a courier service called SDA, a utility company called Enel and, more recently, the mobile operator Telecom Italia Mobile.

"Some of TorrentLocker’s social engineering tactics are consumer-focused, as exemplified by bogus speeding fines sent by the Australian Federal Police (AFP) in Australia," the Trend Micro researchers said. "However, most of the lures are compatible with business targets, such as parcel notifications, which are an important part of a small business’ day-to-day activity. In short, TorrentLocker targets both consumers and SMBs."

Another indication that businesses are now the primary target is that ransomware spam campaigns are timed to coincide with the start of the work day in different regions. Based on Trend Micro's data, most people click on the malicious ransomware links between 9am and 1pm when they would normally be at work.

The cybercriminals behind these operations are also increasingly adding detection evasion techniques, the Trend Micro researchers said.

For example they're using legitimate, but compromised websites to redirect users to the final landing pages. They're also adding CAPTCHA tests to their spoofed sites in order to block automatic crawlers or security sandboxes from catching the malicious payloads.

Some recent TorrentLocker versions even have self-destruct capabilities to prevent IT staff from collecting samples from infected systems.

"We believe that ransomware will continue to improve its tactics and target more business environments," the Trend Micro researchers said. Simple things like verifying the source of emails and the reputation of websites before visiting them can go a long way to prevent ransomware infections. However, the importance of backing up data using the 3-2-1 rule -- at least three copies in two different formats with one copy stored off-site -- cannot be stressed enough, they said.