In a hard-hitting attack, he also alleged that NaMo App secretly records audio, video, contacts and even tracks location via GPS.
Gandhi said if the Prime Minister wants to use technology to communicate with people, he should use the official PMO app.
"Modi misusing PM position to build personal database with data on millions of Indians via the NaMo App promoted by Govt. If as PM he wants to use tech to communicate with India, no problem. But use the official PMO APP for it. This data belongs to India, not Modi," Gandhi said in a tweet.
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"Modi's NaMo App secretly records audio, video, contacts of your friends and family and even tracks your location via GPS. He's the Big Boss who likes to spy on Indians. Now he wants data on our children. 13 lakh NCC (National Cadet Corps) cadets are being forced to download the app," he added.
The Congress chief's remarks comes after the Bharatiya Janata Party (BJP) earlier on Monday accused the Congress of sharing users data with a Singapore-based firm.
Earlier, the BJP had accused the Congress of compromising national security by roping in London-based political data analytics firm Cambridge Analytica to run its 2019 election campaign. The firm is allegedly involved in social media data manipulation.