Advocates of network neutrality frequently express concerns that Internet Service Providers (ISPs) will use sophisticated network filtering technologies that facilitate Deep Packet Inspection to track and modify the content of web pages as they are being served to end users.

The ability to modify Internet content at the network level could potentially be abused by ISPs to insert additional advertising into web pages or perform selective, automated censorship. Although no mainstream ISP in North America engages in such practices, proponents of network neutrality have discovered that Rogers—a Canadian cable Internet provider—is trialing similar technology to inject notices to subscribers in regular web content, leading some to fear that more abusive content manipulation may occur in the future.

Lauren Weinstein, the co-founder of a net neutrality advocacy group called People for Internet Responsibility (PFIR), has published an example of one of the notices that Rogers has begun embedding in web pages. The notice informs users when they are close to reaching their monthly bandwidth cap. According to Weinstein, Rogers is using software created by in-browser marketing firm PerfTech, which can easily be used for more odious endeavors. Rogers uses the software to modify web pages as they are being transmitted, adding JavaScript code that causes the notice to display.

"While Rogers' current planned use for this Deep Packet Inspection (DPI) and modification system (reportedly manufactured by 'In-Browser Marketing' firm 'PerfTech') is for account status messages, it's obvious that commercial ISP content and ads (beyond the ISP logos already displayed) would be trivial to introduce through this mechanism," wrote Weinstein.

The screenshot that Weinstein uses to demonstrate the feature is a Google web page, but the notices will appear on any page that the user visits until they either click a link in the message acknowledging that they have seen it or click a link opting out of seeing future subscriber notices embedded in content.

We asked Rogers for additional information about the subscriber notification system and other potential instances of content manipulation. Rogers confirmed that the notices are being added to pages, but denies plans to engage in more extensive content manipulation. "Rogers has had bandwidth limits on its various tiers of service for several years we are looking at ways to notify customers when he/she hits the 75% mark of that limit," Rogers communications VP Taanta Gupta told Ars. "We do not interfere with the content of the search (it could easily have been a Rogers yahoo search or any web site visit so is certainly not specific to any search engine or web site). This is a trial to make it easier for our customers to keep track of usage. There is no deep package inspection and there is no privacy issue."

Despite the fact that the message is exclusively a notice to subscribers about the service rather than commercial content, some proponents of network neutrality believe that third-party modification of web content—particularly at the ISP-level—fundamentally changes the nature of the Internet in detrimental ways.

"Will Web service providers such as Google and many others, who have spent vast resources in both talent and treasure creating and maintaining their services' appearances and quality, be willing to stand still while any ISP intercepts and modifies their traffic in such a manner?" Weinstein asks, referring to a screenshot of a Rogers subscription information notice plastered onto the top of a Google page. "Google didn't give this ISP any such permission. The ISP simply decided to modify Google on their own."

Although embedding subscription notices in web pages isn't exactly malicious behavior, the use of this practice by Rogers adds credibility to some of the concerns voiced by network neutrality advocates. Rogers already engages in several questionable practices, like impeding the usage of peer-to-peer traffic on its network.

At this stage in the network neutrality debate, when lawmakers and consumers are becoming more aware of the issues at stake, it seems particularly foolish for an ISP to do something that contributes to the credibility of those arguing for stricter regulation. Cable providers appear to be a particularly audacious bunch. Comcast's questionable activities, for instance, are also inviting a regulatory smackdown.