Locky, one of the most popular ransomware families at the moment, has changed its distribution method once again and is now using DLLs for infection, Cyren researchers warn.
The downloader script features a similar structure to the previously used Locky downloaders, as well as a similar behavior: the downloaded files are decrypted and saved in the Windows Temp directory. However, the malicious payload is not an EXE binary as before, but a DLL file, Cyren reports. The dropped DLL is loaded using rundll32.exe.
Upon closer inspection, researchers discovered that the DLL is using a custom packer to prevent anti-malware scanners from detecting it. When executed, the file does the usual ransomware routine to search the affected system and network shares for files to encrypt.
Encrypted files are appended the .zepto extension, and, as soon as the encryption process has been completed, the malware drops and displays a ransom payment instruction page.
According to researchers, the .onion link displayed in the ransom note directs victims to the same Locky decryptor page that has been used in previous infection campaigns as well.