On a recent press trip I was surprised to hear that my online activity was being monitored by Enterasys as I visited the firm’s headquarters in Salem, New Hampshire.

The networking company’s director of strategic alliances in the EMEA region, Mark Pearce, proudly told a table of journalists over lunch that Enterasys’ OneFabric network monitoring software – sold to companies all over the world and used in the Enterasys office to monitor its own employees – could reveal which devices and applications people on the network were using.

A beta version of the the next version of the software, currently being trialled at the Enterasys office, is also able to show which websites people are visiting.

As shocked as I was to learn that our online movements were being tracked, a table of journalists isn't really a big deal compared to a stadium full of paying customers. 

Enterasys has installed its hyper dense WiFi technology and software defined networking solution at the 68,000-seater Gillette Stadium in the town of Foxborough, Massachusetts.

As a result, the stadium – home to the New England Patriots American football team and several gigs a year (including a recent Taylor Swift concert) – provides American football and music fans with internet access.  

Enterasys claims that users are told what data they are handing over in the user agreement when they connect to an Enterasys network, although I did not see one myself when I signed in at the company’s headquarters.

"At the Taylor Swift concert the [online] interaction was twice as high as at a football game, because the demographic is much younger," said Enterasys CEO Chris Crowell.

"It's the next generation who are driving this and their expectation is to interact socially with their extended community. It's about who you're connected to in your extended family."

The company is said to be in talks with seven Premier League football teams in the UK but stadiums aren’t the only places where Enterasys technology is deployed. Universities, high schools and hospitals are already among Enterasys’ customer base.

Enterasys claims that the level of insight offered by its flagship OneFabric network management software is far greater than that of its competitors, which can typically only bring up an IP or Mac address.

Companies can use this insight to collect data which can in turn be used to deliver targeted marketing and messages.

"Privacy I don’t think is dead but I think it’s for sale," said Enterasys chief marketing office, Vala Afshar. "In my view, I look at my kids and the students we hire here, they’re ok. They’re not as stringent as maybe some of the older generation in terms of privacy." 

Nick Pickles, director of Big Brother Watch, said: "The fact that this data is linked to devices demonstrates how companies continue to seek more intrusive ways to monitor us as individuals, and to collect as much data as possible.

"In reality using public WiFi networks is always going to be a risk to your privacy as operators seek to monetise the data they can gather about the people who use them. It might be buried in legalese near the bottom of the service terms and conditions but to claim consumers are giving their informed consent to this tracking is clearly a major stretch. People need to be clearly told what is happening to their data and how they are being monitored.

"It's yet another reminder that there is no such thing as a free service and the price you're paying is with your privacy."

Enterasys was recently acquired by Extreme Networks for $180 million (£112 million). The deal makes the new company the fourth largest networking firm in the world, according to Crowell, who said last week that he wants to compete more directly with Cisco in the future.