West Bengal Chief Minister Mamata Banerjee on Friday expressed concern about the violation of people's privacy and data security due to possible leaking of Aadhar details and urged the people to be more cautious t prevent data theft.Stating that there are reports of Aadhar cards being easily available from "fictitious agencies against payment of small amounts", she said she feared that such cases would be huge infringement of individual privacy and data security."From the very beginning, I have been voicing my serious concern over violation of privacy due to Aadhar and urging to ensure a foolproof mechanism to ensure security of data," she wrote on Twitter."I would like to request all citizens of the country to be more alert and cautious to prevent data theft and violation of privacy," she added.