Data, stored in MRAM-cells should be protected against misuse or read-out by unauthorized persons. The present invention provides an array of MRAM-cells provided with a security device for destroying data stored in the MRAM-cells when they are tampered with. This is achieved by placing a permanent magnet adjacent the MRAM-array in combination with a soft-magnetic flux-closing layer. As long as the soft-magnetic layer is present, the magnetic field lines from the permanent magnet are deviated and flow through this soft-magnetic layer. When somebody is tampering with the MRAM-array, e.g. by means of reverse engineering, and the flux-closing layer is removed, the flux is no longer deviated and affects the nearby MRAM-array, thus destroying the data stored in the MRAM-cells.