Sen. Patrick Leahy, the sponsor of a controversial Hollywood-backed copyright bill, has bowed to public pressure and will yank the most controversial sections from the legislation.

The Vermont Democrat, a longtime ally of large copyright holders, said today he would delete portions of his Protect IP Act that mandate Domain Name System (DNS) blocking and redirecting.

Declan McCullagh/CNET

"I'm going to set aside these domain name provisions," Leahy told Vermont Public Radio. "That we'll hold back on, because I've listened to some of the concerns on those. I think there [are] easy answers to it, but let's set it aside, let's spend a year or so studying that part." (See CNET's FAQ.)

Leahy's volte face has thrown an unexpected obstacle in front of the Motion Picture Association of America and the Recording Industry Association of America--which have lobbied for a bill to censor "rogue" offshore Web sites--just a few days before the Senate debate on the bill begins on January 24. A Web blackout day to protest SOPA and PIPA is planned for January 18 by sites including Reddit and perhaps even Wikipedia.

In a press release after the radio interview, Leahy said that "this is in fact a highly technical issue, and I am prepared to recommend we give it more study before implementing it."

The MPAA said in a statement this afternoon that it was disappointed in Leahy's decision:

We look forward to working with the Senator and other interested parties in passing a strong bill utilizing the remaining tools at our disposal to protect American jobs and creativity. We continue to believe that DNS filtering is an important tool, already used in numerous countries internationally to protect consumers and the intellectual property of businesses with targeted filters for rogue sites. We are confident that any close examination of DNS screening will demonstrate that contrary to the claims of some critics, it will not break the Internet.

The "will not break the Internet" line is a reference to concerns that technologists, including some of the Internet's creators, have raised about Protect IP and SOPA, especially the portions dealing with DNS blocking.

Internet pioneer Vint Cerf said the legislation amounts to "unprecedented censorship" of the Web, and Internet engineers wrote (PDF) a letter to key House and Senate members saying SOPA and Protect IP are not "technically workable." An open letter from Google co-founder Sergey Brin, Twitter co-founder Jack Dorsey, PayPal co-founder Elon Musk, Yahoo co-founder Jerry Yang, among others, said the blocking techniques are "similar to those used by China, Malaysia and Iran."

At the moment, the most recent version of Protect IP says that anyone running a DNS server can be ordered to take "measures designed to prevent the domain name described in the order from resolving to that domain name's Internet protocol address." (That could, however, be easily bypassed by using the numeric address, such as 64.30.224.118 for CNET.com.)

If the DNS portions are deleted, Protect IP would still target financial transaction providers, Internet advertising services, and providers of "information location tools," or ILTs, including search engines and other Web sites. (ILTs are defined as encompassing "a directory, index, reference, pointer, or hypertext link," meaning many Web sites could qualify.)

Sen. Ron Wyden, who has led Senate opposition to Protect IP and recently warned Internet users there's not much time left to fight the legislation, said today he still planned to filibuster the bill.

"Unfortunately, this announcement to study the DNS provision does not eliminate the clearly identified threat to net security contained within this bill," Wyden said in a statement. "Beyond the DNS provisions, the bill still establishes a censorship regime that threatens speech, innovation, and the future of the American economy."

SOPA, of course, represents the latest effort from the MPAA, the RIAA, and their allies to counter what they view as rampant piracy on the Internet, especially offshore Web sites. It would allow the Justice Department to obtain an order to be served on search engines, Internet service providers, and other companies, forcing them to make a suspected piratical Web site effectively vanish. It's opposed (PDF) by many Internet companies, users, and civil liberties groups.

Leahy's statement also claimed that Internet service providers backed DNS filtering: "I remain confident that the ISPs--including the cable industry, which is the largest association of ISPs--would not support the legislation if its enactment created the problems that opponents of this provision suggest."

It's not quite clear what he meant by that: at least two members of the U.S. Internet Service Provider Association have publicly opposed SOPA (USISPA did not immediately respond to a request for comment). And OpenDNS, a DNS provider, has done the same.

Leahy might have been thinking of the National Cable and Telecommunications Association, which applauded Protect IP last May.

The NCTA represents more than just cable companies, though: media conglomerate Viacom CEO Philippe Dauman is an NCTA board member who also serves on the association's executive committee. And Viacom, of course, happens to own MPAA board member Walt Disney Studios Motion Pictures.

Another NCTA member company represented on MPAA's board: News Corporation/Twentieth Century Fox.

In addition, NCTA's announcement came four months after its largest member, Comcast, merged with NBC Universal--whose University City Studios is yet another MPAA board member.