A US firm is targeting first-year university students by infiltrating their private WhatsApp groups and offering to write essays for £7 a page, the Guardian can reveal.

The firm and a series of anonymous individuals are offering made-to-order essays and have been hijacking new students’ group chats at at least five universities, including four prestigious Russell Group institutions.

The messages, posted on accommodation and course group chats created to help freshers settle into university life, boast that students can “pay after delivery”.

Academics said the practice is extremely concerning. One professor called the tactics employed by essay mills to market to students “abhorrent”.

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The findings come as universities and government ministers have expressed concern about the growth of essay mills, which offer pieces of academic work to order for a fee. They are nearly impossible to detect through anti-plagiarism software.

In 2016, an investigation by the Quality Assurance Agency for Higher Education found there were more than 100 essay mill websites in operation.

In Warwick’s group chat for freshers at Bluebell accommodation, someone linked to the company Quality Papers, which, according to its website, is based in New York, said: “If anyone needs essay help. I’m here for you at £7 per page. Essays, research papers, etc. Pay after delivery.”

The same number appeared in WhatsApp groups for students at Imperial College London, Bath University, Birmingham University and Durham University.

The Quality Papers website said: “We will write all papers from scratch, and we guarantee you that the paper will have 0% similarity index.”

The Guardian approached Quality Papers, which admitted it used WhatsApp groups for marketing the company’s services but the response was not always positive and it was usually removed instantly from about 70% of group chats.

A spokesperson said: “We target universities with high populations to increase our chances of getting clients. We get our phone numbers from online virtual number provider services such as CallHippo, so even if you call our numbers they don’t work [for anonymity]. To get into these groups, we give some students our services at extremely low prices and in return they add us into the groups. If you were wondering if using WhatsApp groups is effective, it is not. We are in over 50 WhatsApp groups but this doesn’t help a lot. Students always think it’s a trap set for them by the school.”

They added: “In a week, we can get about seven to 10 papers to write from all the UK WhatsApp groups … I don’t think our services constitute cheating. I have experience with international students who don’t know English very well so they come for editing and proofreading services only. Others work part-time so they don’t have the time to do all the writing. Some international students cannot even construct a complete English statement yet they are required to write flawless essays”

Anonymous writers, some based in the US, who do not appear to be linked to companies also posted in these groups. In Durham’s freshers chat about classical studies, one person offered essays for a similar price of £7 per page.

Prof Andrew Kincaid, a lecturer at Edinburgh Napier University, said: “The tactics employed by essay mills are abhorrent but it’s clever marketing.”

He added: “It is staggering to me that essay mills are legal in the UK. I’m astounded that we are laggards in dealing with this issue and allowing our reputation to be eroded.”

Kincaid said academics are good at detecting cheating in the form of plagiarism and collusion using certain softwares. He said, however, it can be hard to detect submissions from essay mills as they are often “original bespoke pieces of work”. He said: “The detection then comes down to the skill of the academic to identify unusual submissions.”

Thomas Lancaster, a senior teaching fellow at Imperial College London, said the tactics were deceptive.

He said: “This isn’t an ethical line of business in the first place but it’s disgusting to see what lengths companies will go to to convince students to cheat. These companies are damaging to our entire educational system.”

Lancaster added: “Companies are finding new ways all the time to get access to students … They are setting these groups and people from the company are pretending to be new students … They are befriending students, sending them messages, asking them how their day has been and what they are working on … When it gets to the point when a student indicates they are struggling, or have a deadline, these people are there and saying something like ‘did you know about this company? They helped me when I was struggling’.”

One student, speaking anonymously, said they received several messages on Facebook from someone who tried to befriend them before talking about their professional essay writing service.

Students have also reported being targeted on LinkedIn. Another student, speaking anonymously, said: “I have been approached by people on LinkedIn who provide the service of PHD thesis/academic paper language ‘correction’. I assume this does not constitute any kind of fraud but just a kind of editor, before the editor. It could very quickly become a grey area though,” they said.

The findings come after PayPal announced plans to withdraw services from essay writing firms selling to university students after a recent intervention by the education secretary, Damian Hinds.

A PayPal spokesperson said: “PayPal is working with businesses associated with essay writing services to ensure our platform is not used to facilitate deceptive and fraudulent practices in education. PayPal will continue to diligently review and take appropriate action on accounts found to facilitate cheating that undermines academic integrity.”

It noted that the new stance affects customers globally, not just in the UK.