NEW DELHI: Sniffing a major scam of at least Rs 4,000 crore in the railways, CBI is likely to file a case soon into alleged under-reporting of the actual weight of loaded goods wagons through the manipulation of software by officials.CBI sources said that in the financial year 2012-13, railways transported 1,008 million metric tonnes of freight and earned Rs 85,262 crore through it, which constituted 67 per cent of the total revenue for the period.The goods are required to be weighed at the originating station or en route or at the destination point with a view to plugging the leakage of revenue and to avoid over-loading of the wagons, the sources said.An official in CBI said inputs were received that this system has been manipulated at several places in such a way that over-loading is concealed and weight of the wagon is shown to be within the permissible limit."Highly sophisticated methodology of crime by manipulating the software of the system is suspected," the official said.The sources said it is further suspected that the alleged manipulation has been done through collusion amongst railway officials, private vendors and freight operators."Even a 5 per cent under-reporting of actual weight of freight leads to a difference of Rs 4,263 crore by 2012-13 figures... It is not only causing huge financial loss to the exchequer but also (bringing) corresponding gain to private freight operators and is damaging railway tracks and wagons, thus adversely affecting railway safety," an official said.Railways had in consultation with Research Development and Standards Organisation (RDSO) installed 200 'Electronic In-Motion Weigh Bridges' at various locations across the country to weigh the freight in transit.Six vendors have been roped in by RDSO for setting up the bridges, which automatically measure the weight of goods train wagons passing through them at a speed of 15-km per hour, CBI sources said.The agency recently carried out countrywide searches and surprise checks at major freight traffic points with the assistance of the vigilance department of the railways, CBI sources said.The surprise checks were undertaken in Delhi, Uttar Pradesh, Punjab, Jharkhand, Assam, West Bengal, Odisha, Telangana, Andhra Pradesh, Tamil Nadu, Karnataka, Kerala, Chhattisgarh, Madhya Pradesh, Maharashtra, Goa, Rajasthan and Gujarat, etc.During the surprise operation, CBI found "systematic" under-weighing with the system programmed to give readings which were lower than the actual weight."It was found at some of the locations that the quantum of under-weighing increased with an increase in speed of the rake. The preliminary digital analysis of the forensic image taken at some of the locations has revealed old weighing logs showing past manipulations in weighing," a CBI official said.He said alleged manipulations in entries pertaining to wagon type have been revealed with consequences for the weighing."Systematic manipulation in weighing achieved through tampering of the software, EIMWB hardware, manual entries, etc. leads to significant loss of revenue for the railways," he said.CBI has already secured the locations of the in-motion weighing bridges to prevent the possibility of tampering, the sources said.They said that test runs were conducted with rakes comprising freight wagons carrying different loads to check the accuracy of the readings. Besides, the 'in-motion' weighing was also done at different speeds.CBI secured a forensic image of the hard disk of the weighing system to enable a digital forensic analysis for locating the 'digital fingerprints' (automatic weight logs, etc.) of past manipulation in weighing.Meanwhile, Railways said that it was a joint surprise check by Railways vigilance department and CBI to streamline the system and check irregularities, if any."Railways is working with CBI and will continue to extend all assistance to CBI in the matter so as to unearth the truth and take corrective actions as required," a railway spokesperson said.It is our endeavour to constantly improve operation to bring in efficiency and transparency, he said.