Security around 10 scientists working in sensitive areas has been tightened in the wake of threats from Pakistan-based terror groups. The scientists who have not been identified are working in crucial areas of nuclear, defence and space fields.Official sources said today, following corroboration of the threats, a security review was carried out after which it was decided to enhance the security of the scientists as a precautionary measure. Based on the information from the interrogation of US terror suspect David C Headley and his accomplice Tahawur Rana, whose roles are being probed by the security agencies, security around Bhaba Atomic Research Centre (BARC) and some Bollywood studios in Mumbai have been already tightened.