For this project, I wrote two pieces of Matlab code.  The first was an
implementation of the Kermack-Mckendric epidemiological model (km.m).  This was
implemented so that I would have something to compare my model against.  The
second file, scans.m, contains the code for the model I developed.  

The Kermack-Mckendric code is used as follows:

    y = km(V, I, t_max, eta, gamma, time) 
        V:        Initial number of vulnerable machines
        I:        Initial number of infected machines
        t_max:    Time (in seconds) that the simulation should go to
        eta:      Scans per second per infected computer
        gamma:    1/gamma is the average time a worm can propagate on a host
                        before being removed
        time:     When 0, the time axis on the plot is in seconds, when
                    1 it is in minutes, and when 2 it is in hours

    The result is a vector y where the first column of y is the time steps
    iterated over, the second column is the infected population over that
    time, the third column is the removed population over that time, and the
    fourth columns if the vulnerable population over that time. 

The scanning model code has the following usage:
    y = scans(V, I, t_max, eta, gamma, tau, sigma, time)
        V:        Initial number of vulnerable machines
        I:        Initial number of infected machines
        t_max:    Time (in seconds) that the simulation should go to
        eta:      Scans per second per infected computer
        gamma:    1/gamma is the average time a worm can propagate on a host
                    before being removed
        time:     When 0, the time axis on the plot is in seconds, when
                    1 it is in minutes, and when 2 it is in hours
        tau:      Average network speed in KB/s
        sigma:    Average worm size in KB

    The result is a vector y where the first column of y is the time steps
    iterated over, the second column is the infected population over that
    time, the third column is the removed population over that time, and the
    fourth columns if the vulnerable population over that time.  The fifth
    column of y is the number of computers in the scanned population over
    time.