Web developer Dylan Curran posted a thread on Twitter over the weekend that quickly went viral. He tweeted, "Want to freak yourself out? I'm gonna show just how much of your information the likes of Facebook and Google store about you without you even realising it."
In his series of tweets and an opinion piece in The Guardian, Curran, who told CBSN on Wednesday that he "was basically a nobody before this exploded," outlined the information Google stores on users, ranging from users' location to app usage to their YouTube history.
He similarly highlighted Facebook's collection of personal information, saying the social media giant "has reams and reams of data on you, too."
"This includes every message you've ever sent or been sent, every file you've ever sent or been sent, all the contacts in your phone, and all the audio messages you've ever sent or been sent," he wrote in The Guardian.
Speaking on CBSN Wednesday from Ireland, he noted "there are settings to opt out of [Facebook and Google's] data collection," but "not a lot of people have realized that's there."
He also said that consumers have given up so much data voluntarily that "for the current generation and maybe all generations, so millennials and up, the damage is a little bit done." Facebook and Google "have enough information on us to create an advertising profile for the rest of our lives, and it's enough information that can be used against us, for the rest of our lives."
"I'm not saying that they will, just that that information does exist," he added.
Curran said Google had the equivalent of about 3 million Word documents worth of information stored about him, including every Google search he had made since 2009. He said Facebook stored another roughly 400,000 documents worth of information.
The first tweet in his thread has been retweeted more than 146,000 times since Saturday. It has received more than 228,000 likes.
Ex-NSA contractor Edward Snowden called it "an exquisite breakdown using real-life examples of how @Facebook and @Google exploited your trust to quietly create a decade-long dossier of your most private activities."
Curran said the response and attention he's received in the wake of his tweets have made him think "that there's something going on on a larger scale with the population, where people just don't understand what these products are doing and the potential damage that can happen in the future from just freely using them."
A Google spokesperson said in a statement to CBS News that "in order to make the privacy choices that are right for them, it's essential that people can understand and control their Google data. Over the years, we've developed tools like My Account expressly for this purpose, and we'd encourage everyone to review it regularly."