Security has been tightened at all metro stations and prominent location across Delhi after a series of bomb threats were received via emails, an official said on Monday. Multiple institutions, including the Delhi Secretariat, Delhi Assembly, Red Fort and two schools, received bomb threats emails earlier in the day, which were later declared hoaxes following extensive searches by security agencies. "Our cyber teams are trying to trace the IP addresses using which some miscreants are issuing bomb threats. Such criminals are using Virtual Private Network (VPN) to send emails to mislead police investigation. But our experts will find out the culprits," a senior police officer said. The officer further said that after receiving bomb threats, the police beefed up security arrangements at all the important installations, including Delhi Metro stations. The emails stated "Delhi banega Khalistan" and warned of blasts at the Delhi Army School, Red Fort and metro stations within the next thr