The telecommunications company blocked portions of 4chan over the weekend, sparking an outcry from bloggers. The site, which operates with few restrictions, is used mostly for posting pictures and discussing manga and anime.
On Sunday, 4chan founder Christopher "Moot" Poole advised users affected by the AT&T filter to "call or write customer support and corporate immediately."
On Monday, AT&T acknowledged blocking portions of 4chan, but said it was to prevent a DoS attack that started from IP addresses connected to 4chan from spreading and disrupting service to AT&T customers.
"This action was in no way related to the content at img.4chan.org; our focus was on protecting our customers from malicious traffic," AT&T said in a statement.
AT&T removed the blocks Sunday night, after the threat no longer existed. "We will continue to monitor for denial-of-service activity and any malicious traffic to protect our customers," the company said.
Poole on Monday acknowledged that 4chan had been under a constant DoS attack for the last three weeks, but had been able to keep it in check, until it was detected by AT&T. Poole said he was never contacted by AT&T before it blocked access to the site.
"In the end, this wasn't a sinister act of censorship, but rather a bit of a mistake and a poorly executed, disproportionate response on AT&T's part," Poole said in the 4chan blog.
The incident reflects the sensitivity of many Web users toward censorship on the Internet. News of AT&T's action spread quickly over the weekend among bloggers and tech sites. The 4chan site has minimal rules on content, most of which are posted anonymously, and the site has become a part of Internet subculture.
Among the highest-profile incidents of censorship was the Chinese government's mandate that all computers sold in China include Web filtering software. Government officials later reconsidered and said the software did not have to be preinstalled on all computers.
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