Here are the top 10 points in this big story:
The 10 agencies have the powers of "interception, monitoring and decryption of any information generated, transmitted, received or stored in any computer," according to an order from Home Secretary Rajiv Gauba on Thursday.
Earlier, only the home ministry could scan calls and emails of people. The new order gives that power to the Intelligence Bureau, Narcotics Control Bureau, Enforcement Directorate, Central Board of Direct Taxes, Directorate of Revenue Intelligence, CBI, National Investigation Agency, Cabinet Secretariat (Research and Analysis Wing), Directorate of Signal Intelligence (in Jammu and Kashmir, North-East and Assam only) and the Delhi Police Commissioner.
The agencies can monitor not just calls or emails, but any data found on a computer, with the permission of the home secretary. Importantly, the agencies will also have powers to seize the devices, in the name of national security.
If the service provider or any person in charge of the computer resource refuses to reveal information to these agencies, they can face seven years in jail and a fine.
So the next time one stores some document on the laptop, iPad or phone, and if the government is watching, that data can be accessed by investigating agencies. Critics fear the move is to intercept WhatsApp chats and calls.
Lacerated by critics and opposition parties for what they felt was giant step towards a surveillance state, the home ministry clarified. It said to intercept data, the agencies need the home secretary's permission.
The home ministry also said "no new powers have been conferred to any security or law enforcement agencies", that the idea of authorizing other agencies was partly to "decrease the ministry's workload".
Finance Minister Arun Jaitley also dismissed the controversy. "The authorization given to these agencies were brought to law under the UPA government in 2009. We cannot gain access to anybody's phone or data unless it is related to national security," he said.
But ahead of the national election due by May, the row has escalated. "Converting India into a police state isn't going to solve your problems, Modi Ji," sneered Congress chief Rahul Gandhi.
Samajwadi Party leader Ram Gopal Yadav said with "only a few months left to the national polls, the government should not dig its grave."