Documents newly obtained by the ACLU reveal the extent of surveillance conducted by state and local law enforcement agencies with the assistance of cell phone companies. Most notably, they show that location-based tracking has become ubiquitous, with cell phone companies offering "tower dumps" of everyone who used a particular cell phone tower during a particular time period. At least one police department, worried about public backlash if the extent of such tracking became widely known, has barred officers from disclosing the use of such tracking capabilities to the media.
[...]