can someone please tell me why NOD is not recognised by windows security system and what impact this has on security.
You mean it is not recognised by Windows Security Center . The reason is corrupted Windows management instrument . Read this from NOD32's FAQ to fix it Note ! Before doing the above , make sure your NOD32 is working correctly , is updated and that the system time is correct. The impact is none , Security Center is just an informative system .
Nod32 is shown as Antivirus in Vista. This in a Dutch Vista Home Premium Version, but as you can see......it's there.