Mumbai, April 1 -- The Central Bureau of Investigation (CBI) has launched a probe into a cyber-fraud network that allegedly used bulk, fraudulently obtained SIM cards to target thousands of individuals across the country. The Bihar Police initially probed the case, which the CBI recently took over due to the involvement of accused from other states. According to CBI, the network employed a sophisticated setup involving SIM boxes to convert Voice-over Internet Protocol (VoIP) calls into local calls, thereby masking their origin and bypassing security checks. Using this method, the accused allegedly made over 15,000 calls across India within a fortnight between June and July 2025 from a base in Bihar's Supaul. A SIM box routes international calls through local SIM cards, making them appear domestic, while VoIP technology enables voice communication over the internet instead of conventional phone lines. The CBI recently took over the case from the Bihar Police, citing its inter-state ramifications, and registered an FIR on March 18. "A secret investigation and technical analysis was conducted to determine where and by whom the said illegal SIM box was being operated in Supaul. The investigation revealed that the SIM box was owned by Harshit," an official said. Harshit was arrested by the Bihar police in July 2025. A search conducted at his house allegedly led to the recovery of the black-coloured rectangular SIM box, around 800 SIM cards and various documents including a purported notice from Maharashtra's Nagpur (rural police), according to CBI....