The physical protest was accompanied by an online campaign that saw more than 600 Web sites, including prominent open-source software sites, replace their front pages with a warning about the directive.
Thecenters on the Directive on the Patentability of Computer-Implemented Inventions, which would, critics say, legitimize patents on business processes and on ideas software uses. In the United States, where such patents are allowed, large corporations such as IBM routinely stockpile patents to be used against competitors--usually to the detriment of smaller companies.
Opponents want the directive to be rejected when it comes to a parliamentary vote on Monday. They also want it to be refashioned in more restrictive terms. Economists, software developers, scientists and some large European information technology companies have criticized the directive.
The protest's organizers, which included software developer and digital rights lobbying groups from France, Germany, Belgium, Catalonia, Spain and Denmark, estimated that between 400 and 500 people took part in the demonstration, with 500 the maximum permitted by Brussels police.
The protestors, who carried black balloons, wore black T-shirts with slogans such as "Patent inflation is not a victimless crime," "Protect innovation against software patents" and "Software patents kill innovation" in English and French. Banners read: "Software patents kill efficient software development" and "Innovation not litigation."
For the benefit of onlookers and the news media, protestors carried out a mock funeral before tombstones reading, "Maybe you'll be next!" in French and German.
A troupe of mimes in black masks acted out a parable about software patents, involving a fistfight between a businessman in a suit and a scruffy, young software developer.
The outdoor demonstration was followed by a press conference in the parliament building that featured talks by Henk Barendregt, chair of the Foundation of Mathematics and Computer Science at Nijmegen University in the Netherlands, one of the computer scientists who is petitioning against the directive; Reinier Bakels, an attorney; and Hartmut Pilch, the president of the Foundation for a Free Information Infrastructure (FFII), which helped organize the protest.
Arlene McCarthy, the Labour MEP (Member of the European Parliament) responsible for steering the proposal through the European Parliament, has argued that the directive is necessary to harmonize the patent regimes of the European Union's member states and to give inventors a consistent legal framework for patenting their computer-related innovations.
Some opponents of the directive say they support the idea of software patents, but believe the directive implements them in a way that will create more problems than it solves.
Matthew Broersma of ZDNet UK reported from London.