Law enforcement has long had the ability—a combo of the know-how and the legal authority—to hack private citizens' computers in some circumstances. Until late 2016, federal agents could hack into computers with a warrant—but, for the most part, only computers in the judicial district where the judge approved the warrant. (The U.S. is organized into 94 federal judicial districts, with a district usually covering a few of a state's counties.)
An amendment to Rule 41 of the Federal Rules of Criminal Procedure changed the game, allowing agents to search many more computers in many more places with just one warrant.
Amended Rule 41 lets a judge in one federal district issue a warrant allowing agents to hack into computers in other districts if the locations of the computers have been "concealed through technological means." It also allows for this type of warrant where agents are investigating fraudulent access to computers in many districts. (This kind of "fraudulent access" includes users infecting other people's computers with malware.)
The practical effect of the 2016 changes to Rule 41, according to USA Today, was to allow "federal agents armed with a single search warrant to hack millions of Americans' computers or smartphones at once."
Supporters argue that the expanded authority is necessary for the government to keep up. They don't think, for instance, that the FBI should have to get warrants in all the districts where there are computers that are involved in a complicated criminal enterprise.
Opponents contend that the amended rule can cause officers to "forum shop"—to pick and choose the courts where judges are quicker to issue warrants. They also worry about it being easier for the government to legally hack regular folks, as where the computers of innocent users in a bunch of districts have been infected through a malware scheme.