It has dual seeker; optic tracking and magnetic for detonation. If it loses the guidance (optical), it will fly the (updated) predetermined path and the missile will detonate above the target according to the magnetic sensor. It has EFP or shaped charge warhead (not sure which one), shooting the projectile downwards. Direct attack mode is also available if needed.
This is what 80mm RHA penetration by EFP means: What NLAW does is x8+ times more and from above.

These are killers... Finnish military has fielded EFP off route mines since early 1980s. I guess most of you heard about those nasties during the late phase of Iraqi operation. And EFP anti tank mines since the same time too.
what kind of seeker it has? and how can a top attack penetrate armour? I saw that it explodes above the tank and does not directly hit it.. right?