Rackspace’s dispute is with an IP Nav unit called Parallel Iron, which says it has three patents that cover the open source Hadoop Distributed File System (HDFS). But remarkably, Rackspace didn’t even know that at first; IP Nav contacted Rackspace and told the company it infringed some patents while refusing to even reveal the numbers or the owners of the patents, unless Rackspace signed a “forbearance agreement” to not sue first. (Sometimes companies threatened by patent trolls can file a “declaratory judgment” lawsuit, which can help them win a more favorable venue.)

via Rackspace sues “most notorious patent troll in America” | Ars Technica.