Criteo and the dark marketing arts that are growing ever more sophisticated

In a desperate last-minute search for a christening present for some friends of mine (or, more specifically, their baby) I ended up on some website or other, idly clicking through overpriced objects that were sometimes pink and sometimes blue but never quite what I was after. Having closed the browser window and given the company nothing except a few moments of my time, I was surprised to receive an email from them an hour later noting my interest in various products. What sorcery is this? How did they know?

It was one of those unsettling moments when marketing takes one more step into your personal territory than you're comfortable with; it reminded me of a friend of a friend who received a test drive invitation from a sports car manufacturer that featured a Photoshopped picture of one of its cars parked outside his house. Brrr.

These moments are becoming more frequent as marketing departments get better at targeting us – or, as they would put it, showing us things that are "relevant to our interests". The experience of searching for some underwear on a clothing website and then seeing that same pair of pants appearing regularly on Facebook for a fortnight afterwards is one that many of us are now familiar with, but the first time it happened, those pants represented a Minority Report-style wake-up call. Whoah. How on earth did those pants get there? The answer, of course, is cookies, anonymously tracking our behaviour from site to site and wanging relevant adverts into our eyeline. But there's nothing anonymous about a marketing email that begins "Dear Rhodri", and in this case the paper trail was far from clear.

Some light digging unearthed the fact that the company responsible for this particular dark art is called Criteo, and the MD, John Buss, was happy to talk me through this relatively new technique. It's all legal, all cookie-based, but crucially its database – which learns about me and how I click around websites – anonymously links up with databases of email addresses it has licensed from other companies operating online. A match between the two, along with an assessment that I might be likely to splash some cash, triggers an email.

How did my email address end up in the database in the first place? Well, at some point – and goodness knows how, because I do my utmost not to – I opted in to receive some communications "from selected third parties".

So there you have it. A system designed to remind me about products ("you forgot that you wanted to buy this", read a second email I received from the same company) worked like a dream, but it simultaneously made me a bit cross.

For every person like me who resents intrusive marketing, there'll be many who are thankful for the nudge, and Buss was at pains to point out that a) it's very easy to opt out of receiving any more of these emails, and b), proportionally speaking, not many people do. But our email inboxes feel like very personal spaces, and you'd have to question whether invading them so boldly is a sensible strategy.

Having said that, we'll probably get used to it. One day, we'll probably get used to companies knowing we want things before we even realise it. But the question of whether that's serving our needs in a beautifully efficient way or exploiting us in pursuit of profit will continue to be a fraught one.

Twitter.com/rhodri