Facebook users beware: The company has — yet again — unilaterally changed its mind about its data collection practices. As users should know, that's not a good thing for their privacy.

Earlier this month, the dominant social network announced that it's altering the way it determines which ads to show users of its site. In the past, the company based its ad choices on what users were doing on Facebook — what pages they liked, what links they clicked on.

Now, in addition to using that data, the company will also be taking into account the things users do online or on their smartphones outside of Facebook's website and apps. So if Facebook sees you shopping for laxatives at an online drugstore, visiting an adult-themed site or using an exercise app to track your workouts, it might use that information to serve up ads while you're on Facebook.

The change is only the latest example of the company pushing the boundaries of users' privacy concerns, either by collecting more data from them or by taking more liberties with what it does with their data. It also represents just the latest example of the company crossing a line that it had set out in the past to reassure users concerned about the extent of its data collection practices.

"This what Facebook does," said Jeff Chester, executive director of the Center for Digital Democracy, a consumer advocacy group. "Facebook is going to use multiple ways to track their users and sell them to their advertisers."

Facebook declined to make available a spokesman who could comment on the change. But in a post on its website, the company pitched the move as a benefit for users, saying that it would allow the company to offer users more relevant ads. The company also said that the move would give users more control over what ads they see.

But the change pointed out just how much data Facebook is collecting on its users, much of it likely without their knowledge. It also highlighted — yet again — how Facebook's privacy practices are never set in stone.

And it illustrated just how difficult it can be for Facebook users to protect their personal information and habits — even when they are aware of the company's ravenous data collection.

This is a company, after all, that three years ago agreed to 20 years of oversight to settle a complaint filed by the Federal Trade Commission that alleged that the social networking giant repeatedly misled users about its privacy practices.

Facebook has long tracked users' movements off its site through the use of the "like" button and invisible files embedded in many Web pages. But when consumer advocates in the past raised concerns about what the company would do with that data, the company reassured them by saying it wasn't using the data for targeting ads. But that was then. Facebook has now changed its mind.

The problem with the new program, privacy advocates say, is not just that Facebook might use the information to target you with potentially embarrassing ads. It's also that the type of fine-grained information that Facebook is collecting — which is then tied to the personal information users have given to the site about things such as their age and marital status — can be used by advertisers to potentially make inaccurate conclusions about people. It also can be used without consumers' knowledge or awareness to discriminate against them, offering higher prices to some people or not offering particular services to them at all based on inferences drawn about their finances.

"Decisions are being made about us that we don't necessarily understand or have any control over," said John Simpson, the director of the Privacy Project at Consumer Watchdog, an advocacy group.

To be sure, Facebook has provided users a way to opt out of the targeted ads, but it's not terribly user-friendly. The company has chosen to ignore the "do not track" feature found in all the major browsers.

Instead of simply turning on that feature — or just flipping a switch on Facebook itself — the company is directing users to a site run by the Digital Advertising Alliance, an industry trade group. From there, users can opt out of any number of online ad networks or all of them at once.

That sounds easy enough, but because the opt out choices are set with a cookie — a small file saved in the browser — users will have to repeat that step for each browser on every computer they use to access Facebook. What's more, if they follow the advice given by many privacy advocates and clear their cookies, they'll have to remember to go back to the DAA site and opt out again, because its cookie will have been wiped out with the rest.

To avoid the targeted ads on Android or Apple smartphones or tablets, users will have to wade into their settings and find the option to limit ad tracking or opt out of "interest-based" ads. Even if users take those steps, that doesn't necessarily mean that Facebook won't continue to track them — it just means the company promises not to use that information to serve targeted ads.

"The options provided" for avoiding targeted ads "are hugely insufficient," said Julia Horwitz, consumer protection counsel at the Electronic Privacy Information Center, an advocacy group.

But Facebook users can take other precautions that can potentially block the company's tracking. Browser plug-ins such as Adblock Plus, which is available for both Google's Chrome and Mozilla's Firefox, can be configured to block tracking by social networks. Privacy Badger, a plug-in from digital rights advocacy group Electronic Frontier Foundation, blocks such tracking by default. The trade-off? For better or worse, you may no longer see the Facebook "like" button on your favorite websites.

Consumers can also potentially avoid long-term tracking of their surfing habits by using the Tor browser, which has been configured to not only block tracking tools but also to give users anonymity. Unfortunately, Tor can slow Web surfing to a crawl.

But if you're like me and concerned about what Facebook knows about you, what it's doing with your data and how much more it wants to glean, that may be a small price to pay.

Contact Troy Wolverton at 408-840-4285 or [email protected]. Follow him at www.mercurynews.com/troy-wolverton or Twitter.com/troywolv.