Bitdefender is warning the employees and IT administrators of small and medium-sized businesses (SMBs) to be on the lookout for fake emails designed to distribute information-stealing malware.
According to researchers, the attack starts with an email which informs recipients that their employment with the company they work for has been terminated due to policy violations. To make everything more legitimate-looking, the name of the targeted company may be featured in both the subject line and the body of the email, Bitdefender Security Specialist Bianca Stanescu told SecurityWeek.
The name of the file that’s attached to the phony emails can contain strings like “infringement,” “interruption,” “breach,” “infraction,” “violation,” “term” or “disturbance.” What’s interesting about the attachment is that it’s not a .ZIP file like in many other spam runs. Instead, the attackers are using the ARJ file archiver.
“ARJ-compressed files used to distribute malicious attachments are just starting to become popular and many zip file software programs can easily open them,” explained Adrian Miron, anti-spam researcher at Bitdefender. “Because the compression system is rarely used, spammers very well may think of it as a new method to avoid being detected by traditional security software or email filters.”
Once the attached file is decompressed and executed, the malware drops and opens a clean RTF document containing information on discipline programs and company policy violations.
The threat connects to German, Brazilian or French websites, after which it starts communicating with its command and control (C&C) server to receive further instructions from the attackers. The notorious Zeus (Zbot) Trojan, which enables cybercriminals to steal banking information and login credentials from infected devices, is then downloaded onto infected machines.
Bitdefender has seen several Trojans being attached to the bogus emails. One of them is the downloader detected by the security firm as Trojan.Agent.BFIO. At the time of writing, only 20 of the 53 antivirus engines from VirusTotal detect the threat based on its signature.
The spam emails originate in countries such as Spain, Korea, Germany, the United States, the United Kingdom, France, Italy, Russia, Portugal and Saudi Arabia. Bitdefender experts point out that servers in various countries are most likely abused by the cybercrooks in an effort to avoid being tracked down by law enforcement.
According to Stanescu, most of the targeted companies are located in the United Kingdom, the United States and Germany. The security firm has detected and blocked several hundred infections so far.
In addition to the fake job termination emails, the attackers are also leveraging “overdue invoice” and “fax” spam messages using similar social engineering techniques to distribute the malware.
Such attacks represent a serious threat to SMBs, especially with the rise of the bring-your-own-device (BYOD) trend. Recent studies show that many small and medium enterprises allow their employees to access virtual private networks (VPNs) from their personal mobile devices. A study conducted by Bitdefender earlier this year revealed that 18% of SMBs had still been using Windows XP even after Microsoft ended support for it.
