For several years, Proofpoint researchers have been tracking the use of first-stage downloaders, which are used by threat actors to install other forms of malware during and after their malicious email campaigns. In particular, over the last two years, these downloaders have become increasingly robust, providing advanced profiling and targeting capabilities.

https://www.proofpoint.com/us/threat-insight/post/buer-new-loader-emerges-underground-marketplace