get-childitem . -include *.csproj -recurse -ErrorAction SilentlyContinue | %{
    $_.FullName
    [xml]$proj = get-content $_.FullName
    $modified = 0
    $proj.Project.PropertyGroup |
    where-object { $_.Condition -match 'Configuration.*Platform.*(Debug|Release)' } | %{
        if (-not $_.TreatWarningsAsErrors) {
            $node = $proj.CreateElement('TreatWarningsAsErrors', $proj.Project.NamespaceURI)
            $node.InnerText = 'true'
            $node = $_.AppendChild($node)
            $modified = 1
        }
        if ($_.TreatWarningsAsErrors -ne 'true') {
            $_.TreatWarningsAsErrors = 'true'
            $modified = 1
        }
        if (-not $_.WarningLevel) {
            $node = $proj.CreateElement('WarningLevel', $proj.Project.NamespaceURI)
            $node.InnerText = "4"
            $node = $_.AppendChild($node)
            $modified = 1
        }
        if ($_.WarningLevel -ne "4") {
            $_.WarningLevel.InnerText = "4"
            $modified = 1
        }
    }
    if ($modified -eq 1) {
        $proj.Save($_.FullName)
    }
}