The .z attachment of an email that simulates a legitimate sender contains an exe: the malware. The stolen data is exfiltrated via STMP to the same server as the RFQ campaign.
The cyber security experts: It’s used in many campaigns - from Ursnif/Gozi to IcedID - and different countries at the same time. Furthermore, payloads are changed periodically.
Bleeping Computer cyber security experts: The malware uses a new mail template, and it deploys further modules that steal a victim's mail, spread to other computers, or use send spam.