lecture

http://xkcd.com/792/

password reuse

http://xkcd.com/936/


how come some computers are MUCH MORE COSTLY than others?
power. how much you can do at one time.

speed.
measures in hertz
http://en.wikipedia.org/wiki/Hertz

Gigahertz
http://en.wikipedia.org/wiki/Megahertz_myth

other factors:
RAM -- how much do you have?

swap space -- they will swap data and instructions from RAM to the hard drive and back

Moore's law
http://en.wikipedia.org/wiki/Moore's_law

also, computing speed does seem to continuously increase

Traveling salesman problem

millenium prize
http://www.claymath.org/millennium/

1) Generate all permutations of cities
2) For each, calculate the trip length
3) Go through all those lengths, select the smallest one

This works for 4 cities
only 4! permutations

100 cities?
100!
20,098,468,420,666 years

this is assuming current computer architecture
there are other approaches
multiple CPUs in one computer
parallel computing

Quantum computing
DNA computing
maybe we can solve it that way

Phishing

<a href="http://scamsite.com">www.trustedbank.com</a>
http://en.wikipedia.org/wiki/Phishing