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Ursnif Malware Steals Data, Infects Files in US, UK

Researchers at Trend Micro have observed a spike in the number of Ursnif infections. The most affected countries are the United States and the United Kingdom.

Ursnif is a piece of malware that's utilized by cybercriminals to steal passwords and other sensitive information from infected devices. However, the variant that caused the spike, detected as PE_URSNIF.A-O, is also capable of infecting files, the security firm said.

The United States and the United Kingdom account for 39.35%, respectively 35.51%, of infections. The malware has also been spotted on computers in Canada (19%) and Turkey (1.92%). Education, financial, and manufacturing are among the sectors impacted by the threat, which is distributed with the aid of spam messages and Trojan downloaders.

The Ursnif variant analyzed by Trend Micro infects .PDF, .MSI and .EXE files found on removable and network drives. Unlike other similar pieces of malware, which insert malicious code into host files, PE_URSNIF.A-O embeds the host file into its resource section. When one of the infected files is executed by the victim, the malware drops the original file and opens it in an effort to avoid raising any suspicion.

Another anti-detection technique leveraged by Ursnif involves sleeping for 30 minutes before starting the infection routine. This helps the threat evade sandboxes, which usually monitor suspicious files for only up to 5 minutes to see how they behave.

"The fact that a family known for spyware now includes file infectors shows that cybercriminals are not above tweaking established malware to expand its routines," Trend Micro threat response engineer, RonJay Caragay, said in a blog post. "The expansion into file infection can also be seen as a strategic one. A different file infector type (e.g., appending) requires a different detection for security solutions; not all solution may have this detection."

IT administrators are advised to protect their networks against such threats by paying attention to the way network shares are configured. This includes ensuring that computers don't have full access to the network, and configuring network access to read-only.

Trend Micro products detect infected .MSI files as PE_URSNIF.A1, and infected.PDF and .EXE files as PE_URSNIF.A2.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.