Many people show interest in implanted chips (hackers, criminals, etc.)

RFIDvirus.org talks about how to cause havoc by infecting RFID chips with malicious software:

"Now we get to the scary part. Some airports are planning to expedite baggage handling by attaching RFID-augmented labels to the suitcases as they are checked in. This makes the labels easier to read at greater distances than the current bar-coded baggage labels. Now consider a malicious traveler who attaches a tiny RFID tag, pre-initialized with a virus, to a random person’s suitcase before he checks it in. When the baggage-handling system’s RFID reader scans the suitcase at a Y-junction in the conveyor-belt system to determine where to route it, the tag responds with the RFID virus, which could infect the airport’s baggage database. Then, all RFID tags produced as new passengers check in later in the day may also be infected. If any of these infected bags transit a hub, they will be rescanned there, thus infecting a different airport. Within a day, hundreds of airport databases all over the world could be infected. Merely infecting other tags is the most benign case. An RFID virus could also carry a payload that did other damage to the database, for example, helping drug smugglers or terrorists hide their baggage from airline and government officials, or intentionally sending baggage destined for Alaska to Argentina to create chaos (e.g., as revenge for a recently fired airline employee)."

Imagine the damage that could be done when implanting RFID chips in humans becomes widespread.

RFIDvirus.org has a lot of interesting information about malicious software for RFID chips, including how to write RFID viruses and worms. There is also a page on how to protect RFID chips, but just remember that “hackers” are always going to be busy cracking technology. Your implanted RFID chip will never be 100% “unhackable”.