Copie este texto para o arquivo .xml
<?xml version="1.0" encoding="UTF-16"?>
<Task version="1.2" xmlns="http://schemas.microsoft.com/windows/2004/02/mit/task">
<RegistrationInfo>
<Date>2013-12-27T16:14:52.9378367</Date>
<Author>superuser\MagicAndre1981</Author>
</RegistrationInfo>
<Triggers>
<LogonTrigger>
<Repetition>
<Interval>PT1H</Interval>
<Duration>P1D</Duration>
<StopAtDurationEnd>false</StopAtDurationEnd>
</Repetition>
<Enabled>true</Enabled>
<Delay>PT1M</Delay>
</LogonTrigger>
</Triggers>
<Principals>
<Principal id="Author">
<RunLevel>HighestAvailable</RunLevel>
</Principal>
</Principals>
<Settings>
<MultipleInstancesPolicy>IgnoreNew</MultipleInstancesPolicy>
<DisallowStartIfOnBatteries>false</DisallowStartIfOnBatteries>
<StopIfGoingOnBatteries>false</StopIfGoingOnBatteries>
<AllowHardTerminate>true</AllowHardTerminate>
<StartWhenAvailable>false</StartWhenAvailable>
<RunOnlyIfNetworkAvailable>true</RunOnlyIfNetworkAvailable>
<IdleSettings>
<StopOnIdleEnd>true</StopOnIdleEnd>
<RestartOnIdle>false</RestartOnIdle>
</IdleSettings>
<AllowStartOnDemand>true</AllowStartOnDemand>
<Enabled>true</Enabled>
<Hidden>false</Hidden>
<RunOnlyIfIdle>false</RunOnlyIfIdle>
<WakeToRun>false</WakeToRun>
<ExecutionTimeLimit>P3D</ExecutionTimeLimit>
<Priority>7</Priority>
</Settings>
<Actions Context="Author">
<Exec>
<Command>"C:\Program Files\Windows Defender\MpCmdRun.exe"</Command>
<Arguments>-SignatureUpdate -MMPC</Arguments>
</Exec>
</Actions>
</Task>
e importe-o no agendador de tarefas e execute como SYSTEM
. Aqui a atualização é executada em segundo plano silenciosamente. Edite o acionador / configurações como você deseja.