The Enforcement Directorate is already looking into the financial aspect of the matter, sources said.

The scam was the mastermind of a US national who has fled the country. The authorities have arrested some of the employees of his company, Cyberfast Network Systems Corporation, involved in the hi-tech fraud.

The department of telecom has also taken several steps to prevent misuse of leased lines taken by international private lease line circuit operators, mostly for software exports, from Videsh Sanchar Nigam Ltd.

The DoT has intensified surpise checks and inspections. The contract conditions between VSNL and international private lease line circuit operators has also been tightened. A task force comprising technical officers is being set up to detect misuse of leased lines. DoT is also taking steps for effective checking of bonafides of lease line circuitoperators.

The Federal Communication Commission of USA has been approached for help in checking the call-back operations, sources said.

The scandal first came to the notice of the Central Economic Intelligence Bureau (CEIB) which alerted Directorate of Revenue Intelligence (DRI) and Enforcement Directorate. DRI has seized the equipment used by the US national as his offices in Delhi, Mumbai and Chennai.

Cyberfast had taken over 20 telephone connections from Mahanagar Telephone Nigam Ltd. The sophisticated computerised system installed at the company's offices was hooked up to a US telephone service provider. A caller from India would have to dial up the local number of the company followed by the phone number of the person he wishes to talk to in the US. The computerised system would automatically link up the caller to the person in the US.

This operation caused a massive loss to the VSNL, estimated to be over Rs 400 crore in the case of Cyberfast Network System alone. VSNL charges about Rs 15 lakhper year for an international leased line. Cyberfast is understood to have put through over 60 lakh calls in 18 months from Delhi alone. Since the company was using the international leased lines for telephony, which are actually allotted for data transfer, it was able to offer international telephone services to consumer for a much lower price than the normal international call made through the VSNL network.