India, Jan. 4 -- Elaborate network of "ghost" SIM cards and encrypted applications were used by highly educated doctors to stay in touch with Pakistan-based handlers, officials in the know of the Investigations into the "white-collar" terror module linked to the blast near Delhi's Red Fort on November 10 last year revealed on Sunday.

Findings from this probe formed the basis of a major directive issued by the Department of Telecommunications (DoT) on November 28, requiring app-based communication platforms such as WhatsApp, Telegram and Signal to remain continuously linked to an active physical SIM card in the device, news agency PTI reported on Sunday.

The blast occurred on the evening of November 10 when a Hyundai i20 car exploded nea...