I Downloaded the Information That Facebook Has on Me. Yikes.

When I downloaded a copy of my Facebook data last week, I didn’t expect to see much. My profile is sparse, I rarely post anything on the site, and I seldom click on ads. (I’m what some call a Facebook “lurker.”)

But when I opened my file, it was like opening Pandora’s box.

With a few clicks, I learned that about 500 advertisers — many that I had never heard of, like Bad Dad, a motorcycle parts store, and Space Jesus, an electronica band — had my contact information, which could include my email address, phone number and full name. Facebook also had my entire phone book, including the number to ring my apartment buzzer. The social network had even kept a permanent record of the roughly 100 people I had deleted from my friends list over the last 14 years, including my exes.

There was so much that Facebook knew about me — more than I wanted to know. But after looking at the totality of what the Silicon Valley company had obtained about yours truly, I decided to try to better understand how and why my data was collected and stored. I also sought to find out how much of my data could be removed.

How Facebook collects and treats personal information was central this week when Mark Zuckerberg, the company’s chief executive, answered questions in Congress about data privacy and his responsibilities to users. During his testimony, Mr. Zuckerberg repeatedly said Facebook has a tool for downloading your data that “allows people to see and take out all the information they’ve put into Facebook.” (Those who want to download their own Facebook data can use this link.)

But that’s an overstatement. Most basic information, like my birthday, could not be deleted. More important, the pieces of data that I found objectionable, like the record of people I had unfriended, could not be removed from Facebook, either.

“They don’t delete anything, and that’s a general policy,” said Gabriel Weinberg, the founder of DuckDuckGo, which offers internet privacy tools. He added that data was kept around to eventually help brands serve targeted ads.

Beth Gautier, a Facebook spokeswoman, put it this way: “When you delete something, we remove it so it’s not visible or accessible on Facebook.” She added: “You can also delete your account whenever you want. It may take up to 90 days to delete all backups of data on our servers.”

Digging through your Facebook files is an exercise I highly recommend if you care about how your personal information is stored and used. Here’s what I learned.