The emergence of ransomware—a type of malware that prevents or limits its victims from accessing their own files and systems—has become a growing problem for the computing public through the years. Its continuing evolution from “scareware” to a more sophisticated form of malware with encrypting capabilities has made ransomware one of the most notorious malware types to prey on unsuspecting users.
In the first quarter of 2015, we have noted how ransomware has spread to enterprises and niche users. The second quarter then showed an apparent rise in CryptoWall-related URLs. The data collected shows that almost 70% of incidents hit mostly small and medium-sized businesses, followed by enterprise and the consumer segments.
TorrentLocker is a crypto-ransomware strain that has amassed victims in North America, Europe, and Australia, using file encryption to force users to pay a ransom in exchange for regaining access to their kidnapped files. In 2014, we zoomed in on TorrentLocker attacks in Australia and detailed the malware’s usual attack scenario and infection chain.
Our continuing investigation, as seen in the paper “1H TorrentLocker Landscape: Targeting Even More Victims in Australia”, provides more details on the infections seen in the first half of 2015, including common evasion techniques, and solutions to defend against the threat.
Slipping through security cracks
The continuing surge of TorrentLocker may be attributed to the fact that it has successfully devised evasion techniques that allowed it to stealthily infect one’s system. Some of these techniques, as noted below, are known to bypass spam filters, web reputation, and malware detection.
[Watch: TorrentLocker in action]
TorrentLocker sends emails only to legitimate accounts via carefully-crafted email spam. These messages are disguised as actual parcel tracking and penalty notice emails with attached hyperlinks. Instead of using botnets, it uses legitimate web servers to circumvent IP reputation filters. Aside from this, it evades sandboxes by adding a CAPTCHA feature to the malware-carrying web page.
Aside from using standard malware techniques that reduce detection rates, TorrentLocker also inserts dead code, or a sequence of non-effective assembly instructions, that challenge pure signature-based static detections.
Good old bag of tricks
Social engineering lures remained instrumental in the rise of TorrentLocker cases in 2015. The outbreak seen from April to May showed cybercriminals leveraging the Australian Federal Police, and postal services not just in Australia (Couriers Please) but also in Spain (Correos Postal Service). Other data sets noted in the study prove that while the surge of TorrentLocker infections have become a debacle in Australia, it has already started to cross borders and spark concern among users in other countries.
Typically, spam attacks were spotted between 1AM- 9AM, which Trend Micro researchers see as a part of a trick to match email delivery time with the beginning of a work day.
During the course of a study that spanned from April 29 to May 19, Trend Micro researchers monitored TorrentLocker-related URLs seen in different countries. It is not surprising that the results showed that Australia had the highest number of malicious URLs at 63%, reflecting the high volume of the malware in the region. Spain was a far second at 14%, while the United States was third at 6%.
The most effective campaign happened on May 14 in Australia, where data kidnappers used the AFP as a lure. Close to 60% of visits to the spoofed site came from the region, while some Spanish users were also victimized, at 33.6%.
Solutions and Insights
TorrentLocker, much like any other type of ransomware, tricks users into handing over the keys to their most valued data. With the spread of the malware to the enterprise segment, having a solid file backup strategy for home users and businesses is a must. User education and awareness on how TorrentLocker carries out its routines is a good way to keep threats as tricky as this at bay.
There is no silver bullet that can be used to prevent TorrentLocker from causing financial damage and data loss among users and business, which is why it's important to have a holistic, reputation based solution that covers all the bases (web, email, and file). Below are strategies used to prevent TorrentLocker or any ransomware type from entering the enterprise’ system and network:
For the full details and strategies against this ransomware strain, read the paper “1H TorrentLocker Landscape: Targeting Even More Victims in Australia”.
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