A drill resistant lock (30) comprises a bolt member (33) for fitting into a similar sized and shaped slot (35) to secure closure of entry to a property, a locking mechanism (31, 32) associated with a bolt member (33), whereby release and/or closure of the bolt member (33) into the slot (35) is effected by insertion and rotation of an appropriate key in the locking mechanism (31, 32), wherein the bolt member (33) is provided with a core (34) containing a material with different mechanical properties to the main body of the bolt member (33), the material of the core (34) being more drill resistant than the material of the main body.