Comcast has done plenty of things to frustrate subscribers over the years. In fact, some of the company’s recent moves are bad for all of us, not just for its own subscribers. The latest customer complaint making the rounds might be one of the most frustrating ones we’ve seen though, namely because it will likely only impact the savviest of Comcast’s Internet users, and it appears to be completely impossible to prevent.

That’s right, Comcast customers, get ready for an unstoppable wave of spam-like pop-ups in your web browser courtesy of your favorite Internet service provider.

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There is something we have recommended a number of times here at BGR to anyone and everyone with home broadband service: buy your own cable modem. Cable companies make a killing by slapping customers with bogus equipment rental fees that continue forever, long after you’ve covered the value of your cable modem. Then, if you fail to return the modem when you cancel your service, you’re hit with a charge for hundreds more.

It’s ridiculous, and it can easily be avoided by purchasing your own cable modem. A quick one-time purchase of a box like the $70 ARRIS (Motorola) SurfBoard SB6141 DOCSIS 3.0, Amazon’s best-selling cable modem, can end up saving users hundreds of dollars in fees over time. For Comcast customers in certain areas who use older modems, however, using your own box might not be worth the money you’ll save because it looks like you’ll have to endure unescapable harassment as a result.

Comcast has long been injecting code into users’ web browsers to warn them of copyright infringement, and now the carrier is injecting a new kind of pop-up into browsers. Here’s a screenshot:

As reported by Consumerist, users in some regions where services are being upgraded are being encouraged by these injected pop-ups to upgrade their modems so they can receive “the full benefits” of their Xfinity Internet service. That seems harmless enough, right?

Well, here’s the problem: these annoying pop-ups apparently persist until the user has upgraded his or her cable modem to the latest model Comcast offers or to a newer DOCSIS 3.0 modem of their own, and there is no way to opt out. So, if you’ve been saving money by using your own modem and you don’t want to shell out more cash for a newer DOCSIS 3.0 modem — or pay Comcast a monthly fee to use theirs — these pop-ups will become a regular occurrence that you cannot prevent.

In other words, there’s no way to stop the annoying pop-ups without spending money. Oh, and for good measure, Comcast will inject these pop-ups into mobile browsers as well, so you’ll see them on your smartphones and tablets, not just your PCs.

“This feels like a step too far,” wrote the anonymous Comcast subscriber who first revealed these new pop-ups. “It just feels invasive in a way I’m not comfortable with.”

Updated to clarify that any DOCSIS 3.0 modem will stop Comcast’s pop-ups from appearing.