How to collect Security Event Logs for a single category via Powershell

Question

I am trying to write a script which collects security log from all of our domain controllers hourly and stores them remotely; i can collect the security logs , but is there a way to collect the security logs by category or event number from the DC? please do let me know if any additional questions.

My Code:

$Eventlogs = Get-WmiObject -Class Win32_NTEventLogFile -ComputerName $computer
Foreach($log in $EventLogs)
 {
        if($Log.LogFileName -eq "Security")
        {
            $Now = [DateTime]::Now
            $FileName = "Security" +"_"+$Now.Month+$Now.Day+$Now.Year+"_"+$Now.Hour+$Now.Minute+$Now.Second
            $path = "\\{0}\c$\LogFolder\$folder\$FileName.evt" -f $Computer
            $ErrBackup = ($log.BackupEventLog($path)).ReturnValue
            if($clear)
            { 
                if($ErrBackup -ne 0)
                {
                    "Backup failed" 
                    "Backup Error was " + $ErrBackup
                }
            }

        }
    }
         Copy-EventLogsToArchive -path $path -Folder $Folder 
} 

Answer 1

It's not that Get-EventLog doesn't get the Task Category, it's just that it's not the default behavior of the Cmdlet to display it. But the data is still there.

Import-Module ActiveDirectory
foreach($server in Get-ADComputer -Filter *)
{
    Get-EventLog -LogName Security -ComputerName $server | ? { $_.CategoryNumber -EQ 12544 }
}

This is further complicated by the fact that the Task Categories are actually in numerical format - Event Viewer uses CategoryMessageFiles to translate the category numbers into category names.

You can find the location of the CategoryMessageFiles in the registry, at HKLM\System\CurrentControlSet\services\eventlog\Security\Security (there's a subkey for each event log.)

The reason it's done this way is to make it easy for developers to create their own event logs and their own task categories for their own applications.

Here's some developer documentation on how to get CategoryMessage strings, but I know you don't want to go through all that, so the next best thing would just be to find examples of the kind of events that you want to filter for, figure out their category numbers, and then do a Switch($_.CategoryNumber) on them to translate them into what ever strings you like.

Edit: Actually scratch all that. Ignore everything I just said. This should serve you much better:

Get-WMIObject -Query "SELECT * FROM Win32_NTLogEvent WHERE LogFile='Security'" | Select EventCode, CategoryString

Answer 2

Sorry to break this to you but you can't do that (backup a filtered event log file to a new event log file) from the command line in Windows Server 2003.

You can export a subset of the events in an event log to XML or a CSV file.

You can use the Get-EventLog and filter all the events on Task Category with Where-Object. As Ryan has already pointed out, although the task category is not part of the default output, it's still there

The following example only works on Windows Server 2003 (R2 included), and returns all Security Log events in the categories "Logon/Logoff" and "Object Access"

Get-EventLog -LogName Security | Where-Object {@("Logon/Logoff","Object Access") -contains $_.Category}

This is easy to read and maintain, but doesn't perform very nice, since PowerShell fetches and serializes ALL event log entries, before filtering.

Building on Ryans example, let's use a WQL filter to accomplish it instead:

$events = Get-WMIObject -Query "SELECT * FROM Win32_NTLogEvent WHERE LogFile='Security' AND (CategoryString = 'Logon/Logoff' OR CategoryString = 'Object Access')"

To save the filtered events to file you can either export them as rows in a CSV file:

$events | Export-Csv C:\myEvents.csv -NoTypeInformation

or (if you have no problem compressing the backup but would like to keep message formatting) use the Export-CliXML cmdlet to output it to XML:

$events | Export-CliXML C:\myEvents.xml

You can then import them to the command-line when you need to search through them in the future:

$events = Import-CliXML C:\myEvents.xml

The XML output is serialized and requires a lot of storage, but since security log events are mostly filled with whitespace characters, disk space is easily reclaimed by zipping the files. I get a compression ratio of about 98% with an ordinary zip folder from an XML file containing approx. 200.000 security events.

You might be able to achieve even better compression with 7-zip