A few years ago, the American artists Tyler Jacobsen and Nathan Martin created the online application Barcode Generator that could be used to adjust the barcode on products in chain-stores (exemplified as Wal-Mart). The idea being that people should only pay what they felt was right, rather than paying the (over)price determined by the stores.
Barcode Generator was available at the website www.re-code.com but it didn't take long before the artists came under attack from Wal-Mart attorneys who forced them to remove it from the site.
Now the London based product designer Bahbak Hashemi-Nezhad has come up with a (slightly related) hack called Shiv Card, which can be used to evade the fare on London buses.
Shiv Card is made from a recordable greeting card that mimics the feedback sound of an Oyster Card when waved at the electronic reader, thereby fooling the bus driver into believing that the card is real (Oyster Card = electronic ticket/smart card).
Bahbak is a designer who experiments with the boundaries of product design, but since his website only contains limited information it's hard to tell precisely what the artistic motivation behind the project is. From my point of view, the interesting thing about Shiv Card is not the free rides that you get but the anonymity that it provides. Oyster Cards are embedded with RFID chips, meaning that the users' movements within the public transportation grid is likely to be tracked and stored somewhere.
I don't know exactly how the Oyster system works, but another way - and without cheating anyone - of avoiding being tracked, could perhaps be to meet up with other commuters and agree to swap Oyster Cards thereby jamming the data and preventing it from being (mis)used. At least, that's what people in The Netherlands (including myself) did a few years ago when they found out that supermarket-chain Albert Heijn was spying on their customers by data mining the discount cards that they so generously gave away for free.