Submitted by Mike Krieger via Liberty Blitzkrieg blog,

I’m sure you’ve always wondered why pretty much every retailer unnecessarily asks you for your email address at checkout. For years, I’ve always declined and will definitely continue to do so, particularly after reading the following.

From GeekWire:

Another day, another reminder that companies don’t really have to abide by promises to not share your personal information. They have a big “but” in their contracts.

Last week, it was WhatsApp and Facebook. We’ll get to that in a moment.

This week, millions of Sports Authority customers began receiving notices that their e-mail addresses and other data were about to be transferred to competitor Dick’s Sporting Goods. The transfer is legal because Sports Authority declared bankruptcy and sold off its spare parts this summer. Dick’s, smartly and legally, bought the customer information. According to the L.A. Times, a treasure trove of 25 million e-mails and some other data cost Dick’s $15 million. So you might not think your data is valuable, but someone sure does.

First, here is your need-to-know. The transfer is happening right now. You should look for an email from Sports Authority explaining the terms and how to opt-out. Go to SAPrivacyTransferNotice.com and opt out there if you wish.

(Update: Looks like you’ll need a code from the email, which is an unnecessary and consumer-unfriendly hurdle)

But you probably didn’t know that. In fact, when Sports Authority asked for your email, you may have been told, “We won’t share it” by an employee or a web page. Consumers are often told that. It’s a lie, unless it includes the “but,” which is often casually omitted or otherwise missed by consumers.

When Facebook announced it would acquire WhatsApp in 2014 for an astonishing $19 billion, the social media giant promised nervous users it would not suck out their data. Then last week, WhatsApp announced it would, in fact, share phone numbers with Facebook. European regulators are looking into the announcement, and privacy groups have asked the FTC to do the same here in the U.S.

Again, users can opt out, but the process is a bit convoluted. (Click here for an explanation).

What does all this really mean? As privacy researcher Alessandro Acquisti from Carnegie Mellon remarks often, it’s much easier to surrender your privacy than to get it back. The nudges to share information are strong; the fight to protect it or recall it is nearly impossible. So know this: Every time a company asks for your data and tells you it won’t be shared, just assume that’s a lie. Almost certainly, it will be shared or sold or auctioned off some day. If you are fine with that, go ahead and reveal. But do so with your eyes wide open.