Yesterday, Twitter announced its Certified Partners Program. There are currently 12 partners in the program, and they specialize in one of three categories: engagement, analytics, and data resellers. Twitter says that the certifications will “make it easier for businesses to find the right tools.”

As a privacy company, we sat up when we heard the words “data reseller.” Three of the 12 partner companies–Topsy, DataSift, and Gnip–are data resellers, which means they provide access to all publicly available tweet content over several years (what Twitter calls the “Firehose“).

Before data resellers like these existed, your old tweets–even public ones–would become buried as you continued to pile new ones on top of them. They’d be inaccessible after 30 days. Now, companies like DataSift have unlocked this previously inaccessible archive of every Tweet ever made in the past several years. The company collects about 250 million tweets every day, analyzing the things people talk about, the words they use, their geographic location, and even whether their tone seems negative or positive.

Individual tweets may not hold much information about you, but when you consider all of them together, they tell a detailed story. For example, if I saw recent articles you’d tweeted and combined it with who you follow and your retweets, it’s quite possible I could gauge your political views — information that’s very valuable this election year.

Aside from leaving Twitter altogether, there are two ways to protect yourself from Twitter’s data resellers.

1. Go back and delete old tweets.

Unlike when you’re looking for someone else’s Tweets, you can always see your own without any expiration date. DataSift is required to regularly update its files to remove Tweets that have since been deleted.

2. Set your tweets to private by protecting them.

Protected tweets aren’t part of Twitter’s public stream and data resellers can’t collect them. You’ll know that a user’s Tweets are protected when you see a little lock icon next to their avatar.

Protecting your tweets is easy: while logged in to Twitter, click on “Account,” then scroll down until you see “Tweet privacy,” check the box next to “Protect my Tweets,” and hit the blue “Save changes” button on the bottom of the page. Now you’ll have to grant access to people who want to follow you before they can see your Tweet stream.

The announcement comes on the heels of Twitter’s August 16th decision to set new rules for Twitter app developers, which some developers say are too restrictive. Twitter says the changes are for the best, designed to give users a more consistent experience. One change you may have noticed is that tweets from third-party Twitter apps like HootSuite no longer display that they’re from HootSuite.

Twitter has a history of fighting for its users’ privacy, from supporting Do Not Track to challenging law enforcement requests for user’s Tweets, as they’ve done in an ongoing legal battle involving requests for an Occupy Wall Street activist’s Tweets. They’ve also posted a transparency report showing how many times governments have asked them to turn over their users’ data.