Fundamental Rights
(1) No person shall be convicted of any offence except for violation of a law in force at the time of the commission of the act charged as an offence, nor be subjected to a penalty greater than that which might have been inflicted under the law in force at the time of the commission of the offence. (2) No person shall be prosecuted and punished for the same offence more than once. (3) No person accused of any offence shall be compelled to be a witness against himself.
Three separate protections for anyone accused of a crime: (1) you cannot be punished under a law that didn't exist when you did the act (no retroactive criminal laws), and the punishment cannot be harsher than what the law allowed at the time; (2) you cannot be tried and punished twice for the same offence (protection against double jeopardy); (3) you cannot be forced to testify against yourself (protection against self-incrimination).
If a new, harsher law is passed increasing the punishment for a type of online fraud, someone who committed that fraud before the new law existed can only be punished under the older, lighter law that applied at the time - and once acquitted or convicted and punished for a specific act, they cannot be tried again for that same act.