- It's relatively inexpensive and easy to add credit to your paper ticket.
- The Charlie Card is a MIFARE Classic card, subject to at least one well documented attack.
- The cabled data network is exposed; it wouldn't be difficult for someone to eavesdrop on credit card transactions.
Anatomy of a Subway Hack is an interesting look at some of the MBTA's security problems, both physical and electronic. Here are some highlights: