The Stop Online Piracy Act (SOPA), is a bill that was introduced in the United States House of Representatives on October 26, 2011. The bill expands the ability of U.S. law enforcement and copyright holders to fight online trafficking in copyrighted intellectual property and counterfeit goods.

The bill would allow the U.S. Department of Justice, as well as copyright holders, to seek court orders against websites accused of enabling or facilitating copyright infringement. Depending on who requests the court orders, the actions could include barring online advertising networks and payment facilitators such as PayPal from doing business with the allegedly infringing website, barring search engines from linking to such sites, and requiring Internet service providers to block access to such sites. The bill would make unauthorized streaming of copyrighted content a felony. The bill also gives immunity to Internet services that voluntarily take action against websites dedicated to infringement, while making liable for damages any copyright holder who knowingly misrepresents that a website is dedicated to infringement.

Open source software projects may shut down under this bill, under a provision which the EFF believes targets Mozilla, the browser used for about a quarter of all web searches.

“It would cover IP blocking. I think it contemplates deep packet inspection” said Markham C. Erikson, head of NetCoalition, a group that includes Google, Yahoo and eBay. An aide to sponsor Lamar Smith said that the judge would decide what sort of blocking to order.

Andrew Lee, CEO of ESET North America, has expressed concerns that since the bill would require internet service providers to filter DNS queries for the sites, this would undermine the integrity of the Domain Name System. 

Edward J. Black, president and CEO of the Computer and Communications Industry Association, wrote in the Huffington Post that “Ironically, it would do little to stop actual pirate websites, which could simply reappear hours later under a different name, if their numeric web addresses aren’t public even sooner. Anyone who knows or has that web address would still be able to reach the offending website.”

CNET correspondent Larry Downes wrote,

“A bill that was to target only the ‘worst of the worst’ foreign Web sites committing blatant and systemic copyright and trademark infringement has morphed inexplicably into an unrestricted hunting license for media companies to harass anyone foreign or domestic—who questions their timetable for digital transformation.”