[OS X TeX] Job start message question

[Doug McKenna]

Greetings,

Each job I run (using System 10.4, TeXShop 2008 distribution, LaTeX 
format), the console begins with four message lines saying:

 This is pdfTeXk, Version 3.1415926-1.40.9 (Web2C 7.5.7)
 \write18 enabled.
 %&-line parsing enabled.
 entering extended mode

My understanding is that the second line means system commands might be 
executed, representing a security issue.

But I don't understand what the next two lines mean.  The problem with 
searching the web for these phrases is that the vast majority of matches 
are to similar log files, so that didn't help much.

Thanks in advance for any elucidation.


Doug McKenna