The code Louv-Jansen released wasn’t to spy on his friends. “I want people to be aware that they’re leaving some digital footsteps everywhere they go,” he told the Washington Post.

Facebook’s Messenger app, which has more than 800 million active users, is not the only one that tracks when a person was last active. WhatsApp does it too, and it has more than 1 billion users.

“People should be aware whatever they do, they’re not alone, someone is always watching,” Louv-Jansen told the Washington Post. “I don’t want to say that Facebook is evil. This is just a side effect of what they’re doing.”

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