TEL AVIV, May 29 (Reuters) - Israeli police investigating industrial espionage involving leading companies have detained 18 people, including company executives and private detectives, a police spokesman said on Sunday.

The probe by the Tel Aviv fraud squad began several months ago and found evidence that "Trojan horses", viruses designed to spy on computer systems, had been planted in computers of some of the country´s top companies, the spokesman said.

The officials the police are investigating work for firms including Israel´s top mobile phone operator, Cellcom, and two subsidiaries of dominant phone company Bezeq Israel Telecom (BEZQ.TA: Quote, Profile, Research) -- mobile phone operator Pelephone and the satellite television provider YES.

All three companies issued statements saying they were cooperating with the police and had done nothing illegal.

A total of 18 people were detained for questioning including the security managers at Pelephone and Cellcom, who have since been released, and several private detectives suspected of planting the viruses, the police spokesman said.

No charges have been brought.

The chief financial officer of YES is still being held, the spokesman added.

"In this manner of industrial espionage, the private detectives gathered a great deal of information for their clients, who according to suspicions are rival companies," the Tel Aviv police said in a statement.

The police spokesman said two people suspected of creating the Trojan horse, an Israeli who works abroad and his girlfriend, were being held in London and Israel plans to request their extradition.

The Israeli police said they were collaborating with police forces abroad.

COMPANIES DENY BREAKING LAW

YES said in a statement that if the law had been broken, it was against the company´s instructions. It said it believed the investigation would make clear that its chief financial officer had acted according to the law.

Pelephone said in a statement that the company and its employees were not involved in obtaining information illegally.

"The company and its workers were surprised by the latest news and will cooperate with police to clarify the facts of this case," the statement said.

A spokeswoman for Cellcom said the company operates within the law and was cooperating fully with police.

Shares in Bezeq, in which the government recently sold 30 percent to a group that included media baron Haim Saban and British private equity firm Apax Partners, were down 2.8 percent in late afternoon trading, compared with a modest decline on the broader market.

Among the companies infiltrated by the Trojan horse are the HOT cable television group that competes with YES, as well as foodmaker Strauss- Elite (STEL.TA: Quote, Profile, Research) and the Rani Rahav public relations agency, whose clients include Partner Communications (PTNR.O: Quote, Profile, Research) (PTNR.TA: Quote, Profile, Research) , Israel´s second biggest mobile phone operator, police said.

"The Israeli police informed me that one of the suspects used a Trojan horse in a computer," Rani Rahav told Israel Radio. "What we have at the core is a breach of secrets of some of the country´s biggest companies."

Rahav also issued a statement for Strauss-Elite, another of his clients, stating that police presented the company on Friday with material and evidence which the firm is still examining. (© Reuters 2005 05/29/05)