MILAN (Reuters) - Italian police have placed four people under house arrest as part of a probe into alleged illegal access to state databases by a private intelligence business run by a former policeman, a person with direct knowledge of the matter told Reuters.

The person told Reuters that Leonardo Maria Del Vecchio, son of late billionaire Leonardo Del Vecchio, who founded Ray Ban-owner Luxottica, is among those targeted by the probe.

Leonardo Maria Del Vecchio, whom Reuters could not immediately reach for comment, allegedly tasked the intelligence agency with gathering information as Del Vecchio's heirs are in disagreement over the inheritance, the person said. The tycoon died in 2022.

Milan prosecutors allege the business intelligence agency tapped into three key databases: one gathering alerts over suspicious financial activities; one used by the national tax agency with citizens' bank transactions, utility bills, income statements; and the police investigations' database, the person said.

Italy's national anti-mafia prosecutor Giovanni Melillo told reporters on Saturday the probe "rang alarm bells" because it shed light on the "gigantic market for confidential information" which has acquired "a business-like dimension", ANSA news agency reported.

The probe follows another recent investigation into a large-scale data breach at Italy's top bank Intesa Sanpaolo.