# HG changeset patch
# User Christian Urban <christian dot urban at kcl dot ac dot uk>
# Date 1420044202 0
# Node ID 3f0738fc8230dbda363061b1d848a0de8cdc1e70
# Parent  34a8f73b2c9434478e2f6b6b57813c1bf3dbedab
updated

diff -r 34a8f73b2c94 -r 3f0738fc8230 handouts/ho08.pdf
Binary file handouts/ho08.pdf has changed
diff -r 34a8f73b2c94 -r 3f0738fc8230 handouts/ho08.tex
--- a/handouts/ho08.tex	Wed Dec 31 01:49:20 2014 +0000
+++ b/handouts/ho08.tex	Wed Dec 31 16:43:22 2014 +0000
@@ -640,16 +640,41 @@
 \url{http://bitcoinmagazine.com/13774/government-bans-professor-mining-bitcoin-supercomputer/}
 \end{center}
 
-\noindent
-Bitcoin mining nowadays is only competitive, or profitable,
-if you get the energy for free, or use special purpose 
-computing devices.
+\noindent Bitcoin mining nowadays is only competitive, or
+profitable, if you get the energy for free, or use special
+purpose computing devices. 
+
+This about ``free'' energy can actually hurt you very badly in
+unexpected ways. You probably have heard about, or even used,
+Amazon's Elastic Compute Cloud (EC2). Essentially, Amazon is
+selling computing power that you can use to run your web site,
+for example. It is \emph{elastic} in the sense that if you
+have a lot of visitors, you pay a lot, if you have only a few,
+then it is cheap. In order to bill you they, you need to set
+up an account with Amazon and receive some secret keys in
+order to authenticate you. The clever (but also dangerous) bit
+is that you upload the code of your web site to GitHub and
+Amazon will pull it from there. You can probably already guess
+where this is going: in order to learn about Amazon's API, it
+gives out some limited computing power for free. Somebody used
+this offer in order to teach himself Ruby on Rails with a
+mildly practical website. Unfortunately, he uploaded also his
+secret keys to GitHub (this is really an easy mistake). Now,
+nasty people crawl GitHub for the purpose of stealing such
+secret keys. What can they do with this? Well, they quickly
+max out the limit of computing power with Amazon and mine
+Bitcoins (under somebody else's account). Fortunately for this
+guy, Amazon was aware of this scam and in a goodwill gesture
+refunded him the money the nasty guys incurred over
+night with their Bitcoin mining. If you want to read the
+complete story, google for ``My \$2375 Amazon EC2 Mistake''.
+
 
 \subsubsection*{Anonymity with Bitcoins}
 
 One question one often hears is how anonymous is it actually
 to pay with Bitcoins? Paying with paper money used to be a
-quite anonymous act (unlike paying with creditcards, for
+quite anonymous act (unlike paying with credit cards, for
 example). But this has changed nowadays: You cannot come to a
 bank anymore with a suitcase full of money and try to open a
 bank account. Strict money laundering and taxation laws mean