advertising. Users can request that TiVo block the collection of anonymous viewing information and diagnostic information from their TiVo DVR. Litigation TiVo holds several patents that have been asserted against cable TV operators and competing DVR box makers. Opposition by content providers Content flagging In September 2005, a TiVo software upgrade added the ability for broadcasters to "flag" programs to be deleted after a certain date. Some customers had recordings deleted, or could not use their flagged recordings (transfer to a computer or burn to DVD), as they could with unflagged material. The initial showing of this for random shows was a bug in the software. It later was enabled on pay-per-view and video-on-demand content. Pop-up advertisements During early 2005, TiVo began test marketing "pop-up" advertisements to select subscribers, to explore it as an alternative source of revenue. The idea was that as users fast-forward through certain commercials of TiVo advertisers, they would also see a static image ad more suitable and effective than the broken video stream. At its announcement, the concept of extra advertisements drew heavy criticism from subscribers. Some lifetime subscribers were upset that they had already paid for a service based upon their previous ad-free experience, while others argued that they had purchased the service for the specific purpose of dodging advertisements. In 2007, TiVo made changes to its pop-up ad system to show pop-up ads only if the user fast-forwards through a commercial that has a corresponding pop-up ad. In 2019, some TiVo DVRs began running "pre-roll advertisements." These ads are short, but mandatory. The ads run before the user can playback a recorded program. The ads are downloaded from the Internet, so a brief delay occurs before the mandatory ads begin, further delaying playback. Only TiVo DVRs using Experience 4 software (Romio, Bolt, Edge, etc.) have this forced advertising, earlier TiVo software does not deploy pre-roll ads. GNU General Public License and Tivoization In 2006, the Free Software Foundation decided to combat TiVo's technical system of blocking users from running modified software. This behavior, which Richard Stallman dubbed tivoization, was tackled by creating a new version of the GNU General Public License, the GNU GPLv3, which prohibits this activity. The kernel of the operating system of TiVo-branded hardware, the Linux kernel, is distributed under the terms of the GNU GPLv2. The FSF's goal is to ensure that all recipients of software licensed under the