While I flew to Barcelona last week to speak at a conference, my iPad was at breakfast at a restaurant in Cambridge. That, at least, is what I deduced from the device’s location, transmitted to me after I activated the Find My iPhone app on my mobile phone.

I was relieved: the tablet was neither lost nor stolen; it had been accidentally picked up by the organisers of a meeting I had attended the previous day. If, however, another app had found me at the airport and started to badger me with offers, based on my movements, prior purchases and reputation as a loyal or fickle customer, I might have felt a little uneasy.

Here is a question companies increasingly need to answer: what is the creepiness quotient of your product, or marketing campaign, and how would you know? The problem is no secret. Public examples abound. They include embarrassing personalised marketing gaffes — encapsulated in the popular, but possibly apocryphal, tale of the retailer Target, which outed a pregnant teenager to her parents by pitching certain products to her — and the more recent suspension of sales of Google Glass, amid queasiness about the device’s potential misuse. “Problem” may even be a misnomer. While Julia Angwin’s recent book Dragnet Nation describes the dark side of surveillance by companies and governments, a new book by Michael Fertik, founder of Reputation.com, which offers ways of enhancing online reputations, sees it as a simple fact of modern life, which we can exploit for advantage.