The present invention relates to an integrated circuit device containing a memory area, which comprises, on the one hand, a data memory and a program memory, and on the other hand, a program having N code blocks Bi (i=1, . . . , N). It also relates to a method for making such a device secure. The present invention is characterized in that the memory area has M replicas Cj (j=1, . . . , M) of x program code blocks Bi (x=1, . . . , N), which replicas reside at different addresses in said memory area, and in that said device has selection means for randomly selecting one replica Cj of at least one of the x blocks Bi, as a block replica to be used when executing said program. In particular, the present invention can be applied to smart cards.