THE HAGUE (AFP) - Police swooped in 28 European countries and arrested 75 suspects for sharing child sex images on the internet while investigating 207 cases across the continent, Europe's policing agency said Tuesday (Aug 23).

"Operation Daylight" was started after Europol received information from Swiss police last year revealing a vast network of criminals involved in the sexual exploitation of minors, spokeswoman Claire Georges said.

"The investigation lasted for more than a year, based on the Swiss information which led to 611 'intelligence packages' being sent to 26 EU member states," she told AFP. Norway and Switzerland also participated.

So-called intelligence packages have detailed information about suspects and could for instance include information such as computer IP addresses, Georges said.

She confirmed that in many cases, perpetrators used the "Dark Web" and the Tor encryption system to mask their identities.

These paedophile networks "continue to be a primary source for persons with a sexual interest in children who are seeking child sexual abuse and exploitation material online," Europol said in a statement from its headquarters in The Hague.

Although no specific countries were mentioned, Italian police said in a separate statement that many of those arrested were unknown to law enforcement and had never before been outed.

"All above suspicion and many of them older than 50, they secretly contributed to this despicable network from the confines of the four walls of their homes, always paying maximum attention to source the latest material," the statement said.

Georges told AFP that victims varied in age but that there was a worrying and growing trend of sexual abuse of babies under the age of 18 months.

She added the investigation was ongoing and that more arrests were expected.

Europol's EC3 cybercrime centre head Steven Wilson said targeting those involved in child sexual abuse and exploitation material is a "key part" of Europol's work.

"We know that individuals are abusing online platforms and networks to distribute child sexual abuse material and are determined to target them and bring them to justice," Wilson said.

Europol last year said criminals were increasingly selling live streams of child sex over legitimate chat sites and apps such as Skype in return for hard-to-trace virtual currencies like Bitcoin.

In one of the largest busts of its kind, a Europol-coordinated sweep in 2011 identified 670 suspects and 184 arrests were made.