Nicolas Sarkozy's war on illegal downloading has begun in earnest, with the state internet surveillance body dubbed "Big Brother" warning more than 100,000 French internet-users that they have been caught accessing pirate material.

The controversial anti-piracy law is one of Sarkozy's pet projects, backed by his singer wife, Carla Bruni-Sarkozy. The couple argue that artists must be protected from the nation's massive illegal download culture – France is thought to be the world number one in illegally accessing film and music online.

The internet policing system, known under its acronym Hadopi, investigates specific incidents of illegal downloading reported by music and film companies. It obtains web-users' details from internet service providers and issues a series of warnings by email and letter. Repeat offenders risk one month's suspension from all internet access. Those accused of counterfeiting can be fined and cut off from the internet for one year. At least 100,000 warning emails have been sent since early October.

The French left has attacked the law as draconian and against civil liberties. But it is also criticised as ineffective and out of date. The law targets peer-to-peer sites, but not streaming and direct download sites. A study by the University of Rennes earlier this year reported an increase in illegal downloading as web-users turned to new ways of accessing material not covered by the law.

US TV series, such as Grey's Anatomy and House which are increasingly popular in France, are thought to be a key target of illegal downloads.

One magistrate working for the internet surveillance body this week revealed to Le Figaro the pleading letters from illegal downloaders who had received warnings. "It's true, I downloaded an episode of this [unnamed] series. I had no choice, I'd followed the whole season, I was hooked … I won't do it again, but please just let me download the last episode of the series," wrote one man, who had in fact been spotted downloading music.

One woman – told she had illegally downloaded music by the former tennis-star turned singer Yannick Noah – wrote: "I hate that singer. When he played tennis I quite liked him, but his music gets on my nerves." She said an advert flickering across her screen had made her download a track without realising.

One young man said he set his alarm for 6am to download music believing the surveillance system wouldn't be up and running before dawn.