Get-AzureVMAvailableExtension | ft ExtensionName, Publisher

Get-AzureVMAvailableExtension | ?{$_.ExtensionName -eq "VMAccessAgent"}

Publisher                   : Microsoft.Compute
ExtensionName               : VMAccessAgent
Version                     : 2.4
Label                       : Windows Azure Json VMAccess Extension for IaaS
Description                 : Windows Azure Json VMAccess Extension for IaaS
PublicConfigurationSchema   :
PrivateConfigurationSchema  :
IsInternalExtension         : False
SampleConfig                :
ReplicationCompleted        : True
Eula                        :
PrivacyUri                  :
HomepageUri                 :
IsJsonExtension             : True
DisallowMajorVersionUpgrade : False
SupportedOS                 :
PublishedDate               : 5/10/2018 2:28:29 PM
CompanyName                 : Microsoft
Regions                     : All regions

$settingsString = '{"AntimalwareEnabled":true}'
Set-AzureRmVMExtension `
  -ResourceGroupName "[rgName]" -VMName "[vmName]" `
  -Name "IaasAntimalware" -Publisher "Microsoft.Azure.Security" `
  -TypeHandlerVersion 1.3 -ExtensionType IaasAntimalware `
  -Location "North Central US" -settingstring $settingsString