Financial transactions, such as buying and selling, may be facilitated by merchant-based shadow account numbers. A master account may contain several associated shadow accounts. Each shadow account may in turn be associated with a specific merchant or group of merchants. Merchants and users may store and use the shadow account numbers rather than the master account numbers. Stolen or otherwise compromised shadow account numbers are useless with other non-associated merchants. Furthermore, the shadow numbers may be easily invalidated while leaving the master account untouched.