Data, stored in MRAM-cells (12) should be protected against misuse or read-out by unauthorised persons. The present invention provides an array (10) of MRAM-cells (12) provided with a security device (14) for destroying data stored in the MRAM-cells (12) when they are tampered with. This is achieved by placing a permanent magnet (16) adjacent the MRAM-array (10) in combination with a soft-magnetic flux-closing layer (18). As long as the soft-magnetic layer (18) is present, the magnetic field lines (20) from the permanent magnet (16) are deviated and flow through this soft-magnetic layer (18). When somebody is tampering with the MRAM-array (10), e.g. by means of reverse engineering, and the flux-closing layer (18) is removed, the flux is no longer deviated and affects the nearby MRAM-array (10), thus destroying the data stored in the MRAM-cells (12).