Trend Micro CAS - Unexpected file on file share

let f_types = dynamic(['ps1', 'bat', 'scr', 'sh', 'exe', 'js', 'lnk']);
TrendMicroCAS
| where EventCategoryType in~ ('sharepoint', 'onedrive', 'dropbox', 'box', 'googledrive')
| where isnotempty(SrcFileName)
| extend file_type = extract(@'\.(\w+)$', 1, SrcFileName)
| where file_type in~ (f_types) or SrcFileName !contains @'.'
| extend AccountCustomEntity = DstUserName

query: |
  let f_types = dynamic(['ps1', 'bat', 'scr', 'sh', 'exe', 'js', 'lnk']);
  TrendMicroCAS
  | where EventCategoryType in~ ('sharepoint', 'onedrive', 'dropbox', 'box', 'googledrive')
  | where isnotempty(SrcFileName)
  | extend file_type = extract(@'\.(\w+)$', 1, SrcFileName)
  | where file_type in~ (f_types) or SrcFileName !contains @'.'
  | extend AccountCustomEntity = DstUserName  
version: 1.0.0
triggerOperator: gt
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Trend Micro Cloud App Security/Analytic Rules/TrendMicroCASUnexpectedFileOnFileShare.yaml
status: Available
description: |
    'Detects unexpected files on file share.'
queryFrequency: 1h
name: Trend Micro CAS - Unexpected file on file share
kind: Scheduled
triggerThreshold: 0
id: de54f817-f338-46bf-989b-4e016ea6b71b
requiredDataConnectors:
- connectorId: TrendMicroCAS
  dataTypes:
  - TrendMicroCAS
severity: Medium
queryPeriod: 1h
entityMappings:
- fieldMappings:
  - columnName: AccountCustomEntity
    identifier: Name
  entityType: Account
relevantTechniques:
- T1566
tactics:
- InitialAccess