diff --git a/Pilz.Cryptography/UniquieID.cs b/Pilz.Cryptography/UniquieID.cs
index ddf2c08..dad0034 100644
--- a/Pilz.Cryptography/UniquieID.cs
+++ b/Pilz.Cryptography/UniquieID.cs
@@ -72,18 +72,24 @@ namespace Pilz.Cryptography
             return hash;
         }
 
+        private static string Win32_PhysicalMedia_SerialNumber = null;
         private static string TryGetSerialNumberOfFirstHardDrive()
         {
-            var searcher = new ManagementObjectSearcher("SELECT * FROM Win32_PhysicalMedia");
-            var sn = string.Empty;
-
-            foreach (ManagementObject wmi_HD in searcher.Get())
+            if (Win32_PhysicalMedia_SerialNumber == null)
             {
-                if (string.IsNullOrEmpty(sn) && wmi_HD["SerialNumber"] != null)
-                    sn = wmi_HD["SerialNumber"].ToString().Trim();
-            }
+                var searcher = new ManagementObjectSearcher("SELECT * FROM Win32_PhysicalMedia");
+                var sn = string.Empty;
 
-            return sn;
+                foreach (ManagementObject wmi_HD in searcher.Get())
+                {
+                    if (string.IsNullOrEmpty(sn) && wmi_HD["SerialNumber"] != null)
+                        sn = wmi_HD["SerialNumber"].ToString().Trim();
+                }
+
+                Win32_PhysicalMedia_SerialNumber = sn;
+            }
+            
+            return Win32_PhysicalMedia_SerialNumber;
         }
 
         public override string ToString() => ID;