Facebook started testing Express Wi-Fi in India in 2015.REUTERS/Philippe Wojazer

Facebook's user data is the most sought-after piece of information for advertisers. But, it's not just them who hanker after the data; spies and law enforcement officials also want to get access to it time and again. But from now on, it won't be easier for anyone to get those data as the social network issued a new update to its developer policy on Monday (March 13), barring such practices.

According to Facebook, the company's developer rules now prohibit software developers from exploiting its user data to create surveillance tools. The move came as a response to a recent report from the American Civil Liberties Union (ACLU), saying that police were using "invasive social media surveillance software" to spy on activists and protesters in places like San Jose and Baltimore.

"Today we are adding language to our Facebook and Instagram platform policies to more clearly explain that developers cannot 'use data obtained from us to provide tools that are used for surveillance'," Rob Sherman, Facebook's deputy chief privacy officer, said in a post on the social network on Monday.

Sherman also said that using Facebook data for surveillance was always against the company's policies, but it was not explicit enough.

"Our goal is to make our policy explicit," Sherman said. "Over the past several months, we have taken enforcement action against developers who created and marketed tools meant for surveillance, in violation of our existing policies; we want to be sure everyone understands the underlying policy and how to comply."

Sherman did not specify whether law enforcement using Facebook data triggered the policy update, but he said that the company had been working with the ACLU and advocacy groups on this update and to "bring public attention to this important issue."

Meanwhile, the ACLU welcomed the move and said the coalition of advocacy groups would continue pushing for robust systems to ensure that rules protecting the users against surveillance are followed.

"When technology companies allow their platforms and devices to be used to conduct mass surveillance of activists and other targeted communities, it chills democratic dissent and gives authoritarianism a license to thrive. It's clear there is more work to be done to protect communities of color from social media spying, censorship and harassment," Malkia Cyril, executive director and founder of the Center for Media Justice, said in a statement.