The exposure of email addresses of important or famous people has been getting the most attention in this attack, but the breach of SIM card serial numbers (which are related to ICC-IDs and IMI numbers used in the cellular system) is potentially much more significant. These numbers are used for determining the location of the cell phone/device and could put people at higher risk of having their locations tracked by unknown persons via their cell phones. In order to track a SIM card the attacker would need access to the cellular network, but such access could be easily gained and would allow the attacker to track and target an individual cell phone. Enterprises should make sure they are aware of the risk to the physical security of their users who have been exposed as a result of this attack and take precautions, like advising high-risk employees to turn their phones off when not in use.
This was first published in July 2010