The Guardian reported in 2002:
Twenty years after the event, the full truth of the scandal known as France's Watergate may finally come out following a decision this week to send for trial 12 men accused of running a huge, secret and illegal wiretapping operation for François Mitterrand. The Paris public prosecutor's move follows a long inquiry into the activities of the late president's Elysée palace anti-terrorist cell, which on his orders tapped the phones of some 150 people, from lawyers and rival politicians to journalists and an actor, between 1983 and 1986. [...]
Investigators say Mitterrand's anti-terrorist unit was formed secretly in 1982. It began overstepping the mark the following year when lawyers acting for a suspected IRA cell in Vincennes were placed under illegal surveillance, and went wholly off the rails with the Rainbow Warrior affair.
"It seems Mitterrand just became more and more paranoid," one source close to the inquiry said. "Anyone and everyone who looked like posing a threat to his public image had their phones tapped, against the law and against the express instructions of two successive prime ministers."
Among the targets of the eavesdropping campaign was Jean-Edern Hallier, an author and one-time Mitterrand ally who was threatening to disclose the existence of the president's daughter by his mistress. [...]
The scandal, revealed by the daily Libération, first surfaced in 1993. The investigating magistrate, Jean-Paul Valat, battled against a political establishment determined to cover up the affair to the extent of hastily classifying mountains of documents as secrets of state.
The former Socialist prime minister Lionel Jospin finally opened the archives in 1998 - two years after Mitterrand's death - allowing Mr Valat to complete his 400-page case, based in large part on 5,000 incriminating phone call transcripts left anonymously at his office in 1995.
However I can't seem to find a page for this scandal in Wikipedia (well, in English, I found the French one). So what happened in those trials?