"This is no joke as it is on my phone too. I didn't save this number. Check your phone asap, feeling worried," a user tweeted with a screenshot of the saved number.

"How the hell this got into my phone book? If you can do this, then you can read and monitor my activities," another user tweeted.

The Unique Identification Authority of India (UIDAI), however, said that some vested interests were trying to create "unwarranted confusion" in the public and clarified that it had not asked any manufacturer or telecom service provider for providing any such facility.

A French security expert, Elliot Alderson, asked UIDAI on Twitter: "Many people, with different providers, with and without an #Aadhaar card, with and without the Aadhaar app installed, noticed that your phone number is predefined in their contact list by default without their knowledge. Can you explain why?"

Many users later joined in the conversation sharing screenshots of the phone number appearing on their own phones.

"Well, it's true! # UIDAI helpline number got into my phone book magically. They are snooping on us just like NSA in America?" a Twitter user said.

The UIDAI said that the default toll-free number --1800-300-1947 -- being reported to have been included in the contact list of Android phones was outdated and invalid.

"UIDAI's valid toll free number is 1947 which is functional for more than the last two years... UIDAI has not asked or communicated to any manufacturer or service provider for providing any such facility whatsoever," an official statement said.

It emphasised that the said number was not a valid UIDAI Toll free number and some vested interest were trying to create unwarranted confusion in the public.

"UIDAI has reiterated that it has not asked or advised anyone including any telecom service providers or mobile manufacturers or Android to include 18003001947 or 1947 in the default list of public service numbers," it added.

Twitter was abuzz again with the new development after a huge uproar due to Telecom Regulatory Authority of India (TRAI) Chairman R.S. Sharma's open Aadhaar challenge to critics and hackers.

Sharma made a tweetstorm by sharing his 12-digit Aadhaar number on July 28.

Ethical hackers exposed at least 14 personal details of the TRAI Chairman, including mobile numbers, home address, date of birth, PAN number and voter ID, among others.