Microsoft’s Excel 4.0 macros, also known as XL4 macros, became more pervasive in February. The idea of allowing users to create macros that would automate repetitive tasks has been around since Excels very beginnings. Malware authors keep pushing the boundaries, identifying new ways to evade detection, while security researchers try to determine how to better assess Excel documents. Microsoft encourages users to discard Excel macros and migrate to the more modern Visual Basic for Applications (VBA) macros, but many businesses still rely on this benign functionality.”]
Source: https://www.csoonline.com/article/3597913/why-excel-4-0-macro-exploits-are-surging.html