1. A method of controlling the programming of non-volatile memory with configuration data in a programmable logic device, comprising: storing in a plurality of programmable security fuses within the device a multiple bit security pattern; comparing within the device multiple bits of the multiple bit security pattern with multiple bits of a predetermined multiple bit security pattern; if the security patterns match, disabling programming of the non-volatile memory; if the security patterns do not match, determining whether a test bit within the device has been enabled; if the test bit is enabled, disabling programming of the non-volatile memory with the configuration data; and if the test bit is not enabled, enabling programming of the non-volatile memory with the configuration data.