This week we rolled out a change that most people won't notice but for those who do it's a pretty big deal. The change effects those who choose to protect their updates—i.e., only allow those whom they approve follow them.

Previously, if you were protected you had to follow anyone whom you allowed to follow you. Similarly, if you followed someone, you were granting them permission to follow you. This didn't really make sense in a lot of cases. For instance, you may want to get news updates from @bs and others for getting this out.

Earthquake" was trending on Strong quake shakes Southern California" was pushed out by AP about 9 minutes after people began Twittering primary accounts from their homes, businesses, doctor's appointments, or wherever they were when the quake struck. Whether it's updates from best friends, internet pals, companies, brands, or breaking world events, the real-time aspect of sending and receiving Twitter updates continues to motivate our work.

Update: This has been fixed but the actual numbers and profile pictures might not look right until tomorrow afternoon due to caching.

Recently, some people began noticing a decline in their following and follower numbers. We investigated and determined this was caused by an error during a database upgrade. We'll be restoring followers throughout the day to those who were affected and keeping the status blog and Get Satisfaction forum updated with specifics.

Please note that this is unrelated to our ongoing spam initiative as some folks were wondering. Twitter fights spam by putting rules in place to inhibit certain activities. We don't automatically delete accounts en masse.

TwitterCounter is a free service for folks who want to track and share the number of followers they have on Twitter.

Because following another account on Twitter is something you must do with intent, we don't see the same kind of spam normally associated with email—namely, lots of unsolicited Twitter updates in your timeline. However, Twitter has grown popular and thus attracted those who would try to manipulate various features to redirect traffic or gain some other advantage.

We are actively engaged in working to defeat the variety of spam that has made its way to Twitter. The main motivation for spammy behavior on Twitter seems to be the usual: driving web traffic to another site. Some account owners will serially create many accounts and then post thousands of links. Others have only one account but still go crazy posting links—usually to the same web site and often in a way that attempts to trick people into clicking.

A Different Scale

Posting links to Twitter is great and we encourage people to do so. However, spammers are posting links on a whole different scale and they're doing something else we call Aggressive Following. This behavior entails following thousands of other accounts in the hope of reciprocation and it really peeves Twitter users because many of us are sensitive to our Follower count—we don't want email notifications triggered by spammers and we don't want to see our avatar on their profile page.

Those who have created thousands of accounts, posted thousands of the same link, or aggressively followed way too many people, stand out like a sore thumb to our support team because they are usually blocked by hundreds or thousands of well behaved Twitter users. This simple feedback is one of the ways we detect and delete spam accounts but there are also preventative measures and more we could be doing.

Pattern Recognition

By the time spammers show up internally on our blocked list, they've already upset plenty of folks. To deal with spam earlier, we monitor emerging patterns and react with preventative measures. To combat aggressive following directly we have recently imposed new limits on following—spammy accounts following too many users have been drastically curbed. Those that existed prior to this new limit await review. Our administrative tools for finding and dealing with spam grow more sophisticated as we learn more.

The Fight Continues

One thing's for sure, spammers will keep trying to spam. Part of our work will be to keep iterating and evolving our approach to spam so we can provide a good experience on Twitter. Our team has recently expanded to include a Chief Scientist with a keen interest in this area. We just wanted to make sure everyone knows that maintaining a low spam ratio is definitely part of overall service quality.

CEO Jack Dorsey makes it official

letourcongresstweet.org: "Congress should join us where we the people are talking, sharing and networking – online. As Congress reconsiders the restrictions placed on their Internet use, you can tell Congress to embrace the communication technologies that we already use."

Last year, the folks over at Technorati approached us about building something unique to suit their needs regarding search. We created a special real-time feed of every single public Twitter update to be delivered over the open XMPP protocol. Despite delivery over a faster and cheaper technology, this entire public feed of Twitter updates is resource intensive—we had to be very careful about giving it out.

Technorati no longer uses the feed. However, a few other companies have since approached Twitter and made arrangements with us to gain access. There are four services currently accessing our public timeline feed over XMPP: Twittervision, Zappos, FriendFeed, and Summize.

Dave Troy uses the feed to create Twittervision, an intriguing visual display of Twitter updates based on location. Zappos is parsing the feed for updates from its employees and FriendFeed only requires updates from people who use their service—we can be more efficient in serving these companies’ needs. Summize has greatly improved on Twitter’s Track feature by providing a valuable filtering service using our XMPP feed.

Our goal is to support as many applications, projects, mash-ups, and devices as possible so we'll continue to think about how best to do this. While the XMPP feed of the full Twitter Public Timeline is an amazing resource, drinking from the fire hose is not the best way to quench a thirst. With continued updates and refinement, our API will support most scenarios in a way that preserves overall system performance.

The Twitter API is a big part of our success and we will be stabilizing and improving it in the short term. The rate limit is currently set to 20 requests per hour but we’re working to bring it back to 70. Experimentation with XMPP is informing the future direction of our developer platform. Ultimately, our API will be updated and extended to support a wider variety of interesting projects by a great many talented developers.

check out our old office featured in MIT Technology Review (where I stole the title of this blog post).