Scanning uploaded files for viruses

private async Task<UploadedDocument> ScanFile(HttpPostedFileBase fileToScan, string modelProperty)
{
    WebServiceClient MtoaApi = CreateMtoaApi();
    var target = new MemoryStream();
    var fileBytes = target.ToArray();
    
    fileToScan.InputStream.CopyTo(target);
    string fileExtension = Path.GetExtension(fileToScan.FileName);

    bool isInfected = true;

    try
    {                         
        isInfected = await MtoaApi.VirusScanApi.IsInfected(fileToScan.FileName, fileBytes);
    } 
    catch (Exception ex)    
    {
        throw ex;
    }
                       
    // Add error when threat exists
    if (isInfected)
    {
        ModelState.AddModelError(modelProperty, ValidationErrors.FileScanError + $" ({fileToScan.FileName})");                
        return null;
    }

    return new UploadedDocument {
        Name = fileToScan.FileName,
        ContentType = fileToScan.ContentType,
        Data = fileBytes,
        FileNameWithPath = fileToScan.FileName,
        FileSize = fileBytes.Length
    };
}