Operators of a US city transit system were in court Saturday trying to stop hackers from showing thousands of their peers how to get free rides by cracking its fare "smart cards."

Massachusetts Institute of Technology students Zack Anderson, Alessandro Chiesa and RJ Ryan are slated to give an "Anatomy of a Subway Hacking" presentation on Sunday at a notorious annual DefCon conference.

The students had promised to detail how they outwitted magnetic strip and radio frequency chip-based fare cards used in the Boston subway so completely that one could hack their way to "free subway rides for life."

The same smart card technology is used by public transit systems around the world, according to the team.

Boston transit officials filed a suit against the students in federal court on Friday, accusing them of refusing to show them the weaknesses in the computerized fare system and demanding they keep any flaw secret until it is fixed.

"If the discoverer discloses the vulnerability to a broader audience, hackers and other malicious users may be able to exploit the vulnerability," the transit system argues in a court documents.

"It is strongly in the public interest to protect this system."

The suit says another culprit in the case is the students' MIT professor Ronald Rivest, a professor who is also the well-known founder of RSA Data Security firm.

Transit system lawyers on Saturday were trying to convince a federal judge to issue a restraining order barring the students from giving a lecture at DefCon.

They are also demanding a civil trial and want the students to be ordered to pay financial damages.