NEW YORK — Not long after Turkey's prime minister imposed a ban on Twitter, Internet users in Turkey went on — what else? — Twitter to find ways to circumvent the blockade. Twitter Inc. and Turkish news media also shared some tips, as did Turkish residents through low-tech means such as graffiti and street posters.
The response to the ban shows why it's difficult for governments to control the Internet. China and other countries notorious for censoring content have routinely faced efforts by citizens determined to bypass their controls. And in Turkey, people were still tweeting on Friday.
Here's a look at the ban and the ways Turkish Internet users are circumventing it:
Q. Why is Turkey banning Twitter?
A. The ban came as Prime Minister Recep Tayyip Erdogan threatened to "rip out the roots" of the social network. His remarks came after links proliferated on Twitter to recordings that appear to incriminate Erdogan and other officials in corruption. Uproar over the recordings has damaged the government's reputation ahead of local elections this month.
Many people who tried to visit Twitter on Friday got a blocking notice from Turkey's telecommunications authority that referred to four court orders.
Q. How is Twitter being blocked?
A. Internet access providers in the country are redirecting Twitter traffic to a website that contains the blocking notice. It appears that Turkish Internet providers are doing so by changing the numeric Internet Protocol address associated with Twitter.com.
Think of the domain name system as an Internet phone book. When you type in Twitter.com, your computer looks up the numeric IP address for Twitter's website and takes you there. It's similar to the way you can make calls on your smartphone by looking up your friends' names rather than memorizing all the phone numbers.
Turkish service providers can steer you away from Twitter's website by putting an incorrect IP address for Twitter.com in their domain name servers.
Q. How are people still tweeting in Turkey?
A. Users can change the "phone book" their computer uses. The domain name system has multiple copies of these phone books, all of which are supposed to be identical. The Internet access provider usually picks the one used, but users can change settings on their machines to a different one. That way, Twitter.com would pull up the real IP address for Twitter's website.
People also can use masking services called proxies. A person's PC or mobile device connects to the proxy, which uses its own domain name servers to reach out to Twitter on the user's behalf. Turkish access providers know only that the user is reaching the proxy, not Twitter. Instead of a proxy, people can also use virtual private networks, the tools common for accessing secured corporate networks from home. Just like proxies, VPNs reach out to websites on users' behalf. Plenty of free VPNs exist.
Twitter can also be accessed by text messaging. In fact, the reason tweets are limited to 140 characters is to fit the length constraints of texts. Twitter Inc. posted on its Policy account instructions on how to send tweets through texts. The guidelines are in both English and Turkish. It's possible to receive texts on followed accounts as well, though users must enable that one account at a time. Keep in mind that this is a Twitter feature that won't work with other sites that get blocked.
Users also might be able to turn to Twitter aggregation services such as HootSuite. It's similar to a proxy in that the aggregation service is what's making contact with Twitter. The user's computer looks up the IP address for that service, not Twitter. Many of these services let people both post and read tweets.
Q. What's the big deal about the ban if it can be circumvented?
A. These circumvention techniques aren't easy for everyone to carry out. Think of the last time you had to help a tech-challenged friend or relative do something relatively simple, such as attaching a photo to an email.
The government also might step up its blocking efforts, as China does every time a new hole pops up. If people are using HootSuite, the IP address for that website can be changed as well. Proxies and VPNs can be blocked, too. If changing the domain name servers proves ineffective, there are other ways to carry out a ban — including content filtering based on keywords.
Andrew Przybylski, a researcher at Oxford Internet Institute in Britain, said Turkey's techniques so far appear relatively primitive.
"This is Round One of something that could easily escalate," Przybylski said. The domain name system is "the easiest to block, and then the easiest to get around the block. It's more the mindset here."
Online: Using Google's domain name server: https://developers.google.com/speed/public-dns
Twitter's posts on sending tweets by texts: https://twitter.com/policy
Receiving tweets by texts: http://bit.ly/OEUGkn
Electronic Frontier Foundation blog post: https://www.eff.org
Associated Press writers Raphael Satter in London, Suzan Fraser in Ankara, Turkey, and Barbara Ortutay in New York contributed to this story.