Those long-forgotten posts on social networks, from the pasta someone photographed to the rant about her dentist, are forgotten no more. Social networks want to make them easier to find, and in some cases, to show them in ads.

Google on Friday announced that it would soon be able to show users’ names, photos, ratings and comments in ads across the Web, endorsing marketers’ products. Facebook already runs similar endorsement ads. But on Thursday it, too, took a step to show personal information more broadly by changing its search settings to make it harder for users to hide from other people trying to find them on the social network.
Both companies characterized these changes as minor updates. They are, though, the latest example of the continual push by Web companies to collate the reams of personal information shared online in the chase for profits. As Twitter prepares to go public and faces pressures to become profitable, it too will increasingly need to figure out how to make money from the information it collects.
Google and Facebook say that with the most recent changes, they are trying to offer users more comprehensive and personalized services. The problem, privacy advocates say, is when Web companies use or display the personal information of users in ways the authors did not expect when they originally posted it.
“People expect when they give information, it’s for a single use, the obvious one,” said Dr. Deborah C. Peel, a psychoanalyst and founder of Patient Privacy Rights, an advocacy group. “That’s why the widening of something you place online makes people unhappy. It feels to them like a breach, a boundary violation.”
“We set our own boundaries,” she added. “We don’t want them set by the government or Google or Facebook."
Dr. Peel said the rise of new services like Snapchat, which features person-to-person messages that disappear after they are opened, showed how much people wanted more control over how their information was shared.
Still, the biggest Internet companies are pushing in the other direction, toward an expectation that more information is shown publicly. Google’s announcement came in an update to its terms of service that allows the company to include in ads adult users’ profile information and preferences, ratings and posts they have made on Google Plus and other Google services like search and YouTube.
When the new ad policy goes live on Nov. 11, Google will be able to show what the company calls shared endorsements on Google sites and across the Web, on the more than two million sites in Google’s display advertising network, which are viewed by an estimated one billion people. If a user follows a bakery on Google Plus or gives an album four stars on the Google Play music service, for instance, that person’s name, photo and endorsement could show up in ads for that bakery or album.
Such product endorsements, especially from friends and acquaintances, are a powerful lure to brands, replicating word-of-mouth marketing on a broad scale. Social advertising — which includes a wide range of ads, including endorsements — is a $9.5 billion business, according to eMarketer, accounting for 8 percent of digital ad spending.
Many users, though, have strong and skeptical feelings about their endorsements being used in ads without their explicit permission. Facebook learned this the hard way when it was sued in a class action by users who claimed the company had not adequately notified them about how it was using endorsements.
Google may find, too, that by simply following a company or commenting on a post, users might not have meant their actions as endorsements.
“The trick to any advertising like this is to avoid coming across as creepy to your user base and have them say, ‘I didn’t want anyone else to know that,’ ” said Zachary Reiss-Davis, an analyst at Forrester Research.
Google said it would give users the chance to opt out of being included in the new endorsements, and people under the age of 18 will automatically be excluded. If a Google Plus user has shared comments with a limited set of people, only people in that circle will see the personalized ads. Ratings and reviews on services like Google Plus Local are automatically public and can be used in ads, unless a user opts out of shared endorsements.

Don't be evil?