The malware was not a standalone installer, but an archive with a portable IObit License Manager program - one DLL was replaced by malicious unsigned DLL. This DLL dropped DeroHE ransomware to C:\Program Files (x86)\IObit\iobit.dll . This malware was also uploaded to VS via Iobit.rar (packed iobit.dll):
VirusTotal
So, it was probably detected by WD very quickly. The detection is
Program:Win32/Wacapew.C!ml which is (pre-execution) behavior-based detection. The actual signature detection of iobit.dll is Ransom:Win32/Vigorf.A
When this ZIP archive is unpacked with a built-in Windows unpacker, the malicious DLL gets MOTW. So it is checked by WD "Block AT First Sight" after being unpacked. This will prevent the infection of all WD users except maybe the first victim (WD user). Of course, the malicious DLL could be possibly detected by WD behavior-based ML in the cloud, especially with ConfigureDefender HIGH preset.
The malware could be also mitigated by several WD advanced settings. For example, adding exclusions to Windows Defender could be prevented in this particular malware example by the ASR rule
"Block process creations originating from PSExec and WMI commands" "Block executable files from running unless they meet a prevalence, age, or trusted list criteria
" which is present in ConfigureDefender MAX preset.
Anyway, the delivery method is so convincing (trusted IOBIT forum) that in most cases the users simply turn off the protection and install the malware. So, the problem here is not the AV protection but human imperfection.
A good solution for such threats was already presented on MT:
Q&A - Windows Defender Delay Protection. | MalwareTips Community
Edit1.
The malware uses rundll32.exe to run iobit.dll and this behavior is blocked by the ASR rule
"Block executable files from running unless they meet a prevalence, age, or trusted list criteria
".
Edit2.
From the posts made by malware victims, it follows that it could bypass the protection of most AVs (including WD and Kaspersky). But, from the picture above it also follows that these two AVs detected the malware very quickly after the attack.
The users who use 7-Zip or a similar unpacker that does not preserve MOTW, could not be protected very quickly by Windows Defender (default settings) because the Block At First Sight feature was not triggered for the malicious DLL in the IObit License Manager package.
