Tom Lierman focused on hardening the mcuboot bootloader for Zephyr RTOS, addressing a critical bug in the bootstrap copy size calculation for swap move mode. He implemented a fix in the zephyrproject-rtos/mcuboot repository that recalculates the copy length using the secondary region size, excluding the swap sector, to prevent over-copying during image upgrades and bootstrap operations. This change improved upgrade reliability by resolving a regression that could cause failures. Working in C and leveraging his expertise in embedded systems and bootloader development, Tom demonstrated careful attention to memory region handling and maintained code quality through clear documentation and peer review.