Weapons that down threatening drones — by scrambling their electronics or just plain shooting them out of the sky — are flooding the market, even though most are still illegal in the U.S.

What's new: Just in the last year, hundreds of new products were released, in a scramble to head off an urgent unsolved menace. But off-the-shelf drones are evolving apace, threatening to make a thorny problem even worse.

The big picture: As I wrote this summer, plenty of roadblocks still lie ahead for the counter-drone industry. Fundamentally, many anti-drone systems don't work well — and even if they did, most are illegal in the U.S., except if used by federal agencies.

Driving the news: A new report from the Center for the Study of the Drone at Bard College is a comprehensive census of counter-drone technology.

Altogether, Bard researchers found 537 systems for sale — hundreds more than they found in last year's sweep.

More than 350 of these products are billed for intercepting and disabling drones; the rest simply detect them.

Radio jamming is the most popular method for taking down drones. But other creative approaches involve lasers, nets or even a "sacrificial collision drone."

The report raises two new problems. One is the limited range of many detection systems.

"The response time for successfully shooting down drones is incredibly short if the drone is even moderately fast," says the report's author, Arthur Holland Michel.

Even with a 1 km detection range — which may seem far — several steps remain after an incoming drone is detected: a second check, a decision to intercept, a scramble to ready the relevant weapon…

"By that time, the drone is right over your head," Michel says. "You don't hear this discussed in the marketing materials."

The second problem is the rapid progress of consumer drones, which is creating a "vicious feedback loop," Michel says. Advances that make the devices safer can also make them impervious to some counter-drone systems.

The bottom line: "There's nothing on the horizon that will cut the line on this [cycle]," says Michel. "There's nothing that just ends the game. … Until there is, it's going to be like this: a game of cat and mouse."