Security researchers caught a new phishing campaign that tried to deliver the BazarBackdoor malware by using the multi-compression technique and masking it as an image file.
The multi-compression or nested archive method is not new but gained in popularity recently as it can trick email security gateways into mislabeling malicious attachments as clean.
It consists of placing an archive within another. Researchers at Cofense say that this method can bypass some secure email gateways (SEGs), which can have a limit to how deep they check a compressed file.