The police have strengthened Reserve Bank of India Governor Raghuram Rajan’s security following an email threat bearing the name of the dreaded terror outfit, Islamic State (IS), last month. While the source remains untraceable, investigators strongly suspect that the email — demanding money from Mr. Rajan — is a hoax. The police have also sought help from Google, the service provider for the account isis583847@gmail.com using which the alleged email was sent, said sources.