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In our regular, offline lives, we usually play many different roles and adapt to these roles without much thinking. At work, you show your professional self. When visiting friends, you are the social version of yourself. At home, you and your partner might be perfectly happy reading a book without exchanging many words. Back at your parents' place, some childish old habits might suddenly pop up. Similarly, on the web, we have many online identities - probably far more than we have in our regular lives.

I have several social media accounts and on each of them, you will probably get a different impression of me. My Facebook account is largely personal, even though I do publish professional updates as well. My Facebook identity is probably much happier than my real self - simply due to the fact that I, like many others, tend to mainly share positive things that happen in my life. My accounts on LinkedIn and Xing mainly contain my resume and working history, based on which you might come to the conclusion that I am a very serious, perhaps even a bit boring person. I do have a Twitter account, but that one is largely inactive: my tweet history is limited to conferences that I attended. I am also active in the forum of the Dutch vegetarian website Vegatopia (of which I am site admin) and based on my activities there, you probably think that my whole life is centered around food (which, in a sense, is true).

An interesting observation is that in the early days of the web, the 1990s, people would typically act online using a nickname and an avatar. Chatting via ICQ ("uh oh") with like-minded anonymous people from the USA (or anywhere else) was the coolest thing to do - in most cases without any consequences and without actually meeting these people. Gradually, it has become more and more common to use our real names and an actual photo for our profiles. This change definitely did not only take place due to Facebook's controversial real-name policy (which, by the way, recently has been ruled illegal by a German court): the more important reason is that our online lives have become intimately connected with our real lives: we communicate with friends and family, pick a date for a meeting, shop online, manage our money through the internet, and advertise ourselves. For these purposes, it is only natural to use your own 'real' identity.

As an example, in the early days of Vegatopia, the site was run by a team of hobbyists, who preferred to operate (semi-)anonymously. For this reason, all articles and recipes were signed only with the writers' first names. Currently, many of our writers have their own blogs, Facebook account or Instagram page. In contrast to earlier days, it is now in their direct interest to enable them to claim their own work. For this reason, some years ago, we changed our policy and now use the authors' full names, combined with a profile picture.

But our online identities include far more than our social media profiles. If you buy at an online shop without registering, your purchase is processed and after the purchase your one-time identity is gone. If you register at Amazon, you have an online 'buying' identity, which Amazon uses for providing you with recommendations and personal offers. If you did not opt out of Google Ads, you have an 'advertising' identity - which basically involves a general list of your interests. As far as I know, your Google Ad identity is not connected with your Google GMail identity (at least not anymore).

But what about an IP address? According to the GDPR, an IP address is personal data - and, indeed, as discussed in a previous blog post, an IP address can be used for identifying that the person browsing is you (or confuse you with your partner or room mates, who access the web via the same IP address, making use of the home wifi).

For simple one-time transactions, we can make use of one-time identities. Sometimes, we have an online identity (or, rather, a profile) that we only use for a limited time (such as participating at an event, or taking a course). Other online identities remain active for months, years, decades. The longer an online identity exists, the more privacy risks are associated with your identity - and the more useful this online identity probably is.


A temporary GMail account for the sake of finding a lost cat, seen today on my Facebook wall.
Fortunately, in the meantime, the cat has been found, alive and healthy.

When I moved to Nijmegen last year, I could have walked around through the city center more or less anonymously. I could have done something silly or offensive and, if I wouldn't have been caught in the act, I probably would have gotten away with it. Now, one year later, it is already quite likely that I would have been observed by someone who already knows me. In return for this loss of anonymity, I now have friends, nice colleagues, students (generally also very nice), neighbours and other persons I like in this city. This opens opportunities for pleasant evenings, nice chats, inside information and asking for a favour.

Similarly, if you want to sell something online, or if you need to have some sort of a reputation for a transaction, a one-time identity probably will not work. As a first-time seller, it is much harder to find customers than for a person with a positive, long-lasting reputation. If you already have written good reviews, your next review will automatically receive far more attention and credit than a first-time review (see our ICWSM 2017 paper on editorial, temporal and social biases).

If all my different online identities would meet and try to merge into one 'real' identity, this would most likely result in a very incoherent, paradoxical and probably very annoying personality. We all play different roles, we are observed from different angles, and with different intentions. If your partner would have a conversation about you with one of your colleagues, they will probably both learn quite a bit of your 'other' sides, which usually is interesting and funny, but sometimes a bit embarrassing.

I am comfortable about my partner talking with my colleagues during a party, but I probably would not want my Facebook Ads identity to learn interesting things about me from my GMail identity. Some things just need to remain separated.

The title of this blog post was inspired by a 2007 book by the German philosopher Richard David Precht: Wer bin ich und wenn ja, wie viele?

beijing opera

eelcoherder 256px

Privacy Engineering, User Modeling, Personalization, Recommendation, Web Usage Mining, Data Analysis and Visualization, Usability, Evaluation

Dr. Ir. Eelco Herder
Associate Professor
Human-Centered Computing Group
Information and Computing Sciences
Utrecht University

Buys Ballotgebouw
Princetonplein 5
3584 CC Utrecht
The Netherlands