Two days ago, Comcast did something that would be inconceivable if it was any other company than Comcast: It turned 50,000 residential Xfinity modems into public WiFi hotspots. There are 50,000 paying Xfinity customers in Houston, Texas who are now broadcasting free WiFi that anyone can use. As far as Comcast is concerned, of course, this is a genius move to blanket the country in high-speed WiFi (and there are plans to hijack millions more modems by the end of 2014) — for Comcast’s customers, though, this is egregious monopolistic overreach taken to the next level… and it’s possibly illegal as well.

Xfinity WiFi Home Hotspot: Genius or madness?

First, let’s run through the technical details of Comcast’s Xfinity WiFi Home Hotspot setup. Over the last couple of years, Comcast has been distributing the Arris Touchstone Telephony Wireless Gateway Modem to new customers. Comcast remotely programmed these modems to broadcast a new wireless network SSID — “xfinitywifi” — that gives two one-hour sessions per month to anyone, or unlimited access to other Comcast customers. Comcast says the new wireless network is completely separate from your existing home network, and that public WiFi users don’t have access to any shared files or resources. Exact details of the setup aren’t yet known, but it sounds like some kind of VLAN.

Now, let’s tackle the rather thorny questions raised by this scheme. Speaking to the Houston Chronicle, Comcast says this new service won’t slow down the residential customer’s connection. The official Xfinity WiFi Home Hotspot FAQ clarifies a few other points, too, such as the max limit on concurrent free WiFi users (five), and how to disable the feature (log into http://customer.comcast.com/ and click the Users & Preferences section). Comcast says that it alerted the first 50,000 users by post last month, and that less than 1% of customers opted out. It’s also worth noting that you’re exempt from Comcast’s new scheme if you use your own modem, too.

The FAQ does note, however, that “there can be some impact as more devices share WiFi” because both networks share the same slice of 2.4GHz or 5GHz spectrum. From what we know about WiFi congestion and the importance of using the right channel, just having one person using your Xfinity WiFi could significantly slow down your own WiFi network.

Will Comcast Xfinity WiFi slow down your connection to the internet?

The more curious bit is Comcast’s assertion that this public hotspot won’t slow down your residential connection — i.e. if you’re paying for 150Mbps of download bandwidth through the Extreme 150 package, you will still get 150Mbps, even if you have five people creepily parked up outside leeching free WiFi. This leads to an interesting question: If Xfinity hotspot users aren’t using your 150Mbps of bandwidth, whose bandwidth are they using?

There are two options here. Comcast might just be lying about public users not impacting your own download speeds. The other option is that Xfinity WiFi Home Hotspot uses its own separate channel to the internet. This is entirely possible — DOCSIS 3.0 can accommodate around 1Gbps, so there’s plenty of free space. But how big is this separate channel? 50Mbps? 100Mbps? And if there’s lots of spare capacity, why is Comcast giving it to free WiFi users rather than the person who’s paying a lot of money for the connection? And isn’t Comcast usually complaining about its network being congested? At least, that’s the excuse it used to squeeze money from Netflix, and to lobby for paid internet fast lanes.

With 50,000 hotspots enabled in Houston today, 150,000 more planned for the end of the month, and then 8 million more across Xfinity hotspots across the US before the end of 2014, we can only assume that Comcast has a lot of extra capacity. Either that, or it’s intentionally trying to clog up the network for its paying customers — perhaps so it can levy further charges from edge providers like Netflix, or so it has some ammo in the continuing battle for net neutrality. [Read: AT&T moves to acquire DirecTV to defend against Comcast – everyone loses.]

The big picture, of course, is that Comcast wants to compete with AT&T, which already has a large nationwide network of WiFi hotspots. It’s also worth noting that, following a spectrum sale to Verizon last year, Comcast now has access to Verizon’s mobile network. Comcast could be building towards a future mobile telephony system that bounces between free WiFi hotspots and Verizon’s network, depending on what’s currently available.

Is Comcast breaking the law?

Finally, a thought experiment about the legality of Xfinity WiFi Home Hotspot. Comcast owns the Arris Touchstone modem that you rent as part of your monthly subscription, and thus is fairly free to do whatever it likes with regards to setting up a secondary network. It’s a bit crappy, but it’s probably legal (and you probably agreed to such antics when you signed on the dotted line). What is less clear is ownership of the connection between the modem and the wall socket (your cable) and between the wall socket and the junction box (fiber to the curb/cabinet).

You almost certainly own the cable from the modem to the wall, and Comcast is treading on shaky ground by using that cable, especially as the Xfinity residential WiFi rollout is opt-in by default. There have also been instances where FTTC providers pass the buck when there’s issues with the copper wire between your home and the junction box — suggesting that you might own that as well (it runs over your property, at the very least).

I assume Comcast had its legal bigwigs sign off on the plan before moving ahead with the subversion of 8 million paid customer connections. But who knows: Internet providers in the US seem to be able to get away with just about anything.