like the old Wild West. Anything seems to go. 

For example, UCAS, a charity set up to help students to apply

to universities, has a commercial unit that happily sells your

email addresses to anybody who forks out enough money in order

to be able to bombard you with spam. Yes, you can opt out very

often in such ``schemes'', but in case of UCAS any opt-out

will limit also legit emails you might actually be interested

shamelessly sell email addresses they ``harvest''. Everything

Another example: Verizon, an ISP who provides you with

connectivity, has found a ``nice'' side-business too: When you

have enabled all privacy guards in your browser, the few you

have at your disposal, Verizon happily adds a kind of cookie

to your

help with clarifying the overall picture somewhat: 

      anybody's business'.

happy to be a digital exhibitionist: I am very happy to

academia (at least in the field of CS), even expected if you

look for a job. I am even happy that Google maintains a

profile about all my academic papers and their citations. 

On the other hand I would be very irritated if anybody I do

not know had a too close look on my private live---it

shouldn't be anybody's business. The reason is that knowledge

about my private life usually is used against me. As mentioned

above, public location data might mean I get robbed. If

supermarkets build a profile of my shopping habits, they will

use it to \emph{their} advantage---surely not to \emph{my}

advantage. Also whatever might be collected about my life will

always be an incomplete, or even misleading, picture---for

example I am sure my creditworthiness score was temporarily(?)

destroyed by not having a regular income in this country

(before coming to King's I worked in Munich for five years).

To correct such incomplete or flawed credit history data there

is, since recently, a law that allows you to check what

information is held about you for determining your

To cut a long story short, I let you ponder about the two

statements that often voiced in discussions about privacy:

\mbox{}\hfill{}{\small{}by Scott Mcnealy (CEO of Sun)}

\noindent An article that attempts a deeper analysis appeared

in 2011 in the Chronicle of Higher Education

\begin{center} 

\url{http://chronicle.com/article/Why-Privacy-Matters-Even-if/127461/} 

\end{center} 

\noindent Funnily, or maybe not so funnily, the author of this

article carefully tries to construct an argument that does not

only attack the nothing-to-hide statement in cases where

governments \& Co collect people's deepest secrets, or

pictures of people's naked bodies, but an argument that

applies also in cases where governments ``only'' collect data

relevant to, say, preventing terrorism. The fun is of course,

in 2011 we could just not imagine that respected governments

would do such infantile things as intercepting people's nude

photos. Well, since Snowden we know some people at the NSA did

and then shared such photos among colleagues as ``fringe

benefit''.  

\subsubsection*{Re-Identification Attacks} 

Apart from philosophical arguments, there are fortunately also

some real technical problems with privacy implications. The

problem I want to focus on in this handout is how to safely

disclose datasets containing potentially private data, say

health data. What can go wrong with such disclosures can be

illustrated with four examples:

\item In 2006, a then young company called Netflix offered a 1

      containing 10\% of all Netflix users at the time

      (appr.~500K). They removed names, but included numerical

      ratings of movies as well as times of ratings. Though

      some information was perturbed (i.e., slightly

      modified).

      Two researchers had a closer look at this anonymised

      data and compared it with public data available from the

      International Movie Database (IMDb). They found that 98

      \% of the entries could be re-identified in the Netflix

      dataset: either by their ratings or by the dates the

      ratings were uploaded. The result was a class-action 

      suit against Netflix, which was only recently resolved

      involving a lot of money.

\item In the 1990ies, medical datasets were often made public for

      research purposes. This was done in anonymised form with

      names removed, but birth dates, gender, ZIP-code were

      retained. In one case where such data was made public

      about state employees in Massachusetts, the then

      governor assured the public that the released dataset

      protected patient privacy by deleting identifiers. A

      graduate student could not resist and cross-referenced

      public voter data with the data about birth dates,

      gender, ZIP-code. The result was that she could send

      the governor his own hospital record.

\item In 2006, AOL published 20 million Web search queries

      collected of 650,000 users (names had been deleted).

      This was again for research purposes. However, within

      days an old lady, Thelma Arnold, from Lilburn, Georgia,

      (11,596 inhabitants) was identified as user No.~4417749

      in this dataset. It turned out that search engine

      queries are windows into people's private lives. 

\item Genomic-Wide Association Studies (GWAS) was a public

      database of gene-frequency studies linked to diseases.

      you only needed partial DNA information in order to

      identify whether an individual was part of the study —

      DB closed in 2008