Re: Two ways to torture a comp teacher

[christer@cs.umu.se (Christer Ericson)]

In <faddenCttwHJ.FMn@netcom.com> fadden@netcom.com (Andy McFadden) writes:
>[...]
>To keep people from performing dastardly deeds, my high school computer
>lab ran a hacked version of BASIC in the language card.  It disabled
>POKE, PEEK, CALL, and every other command that you could use to disable
>the language card and get into "normal" BASIC, and hence into the system.
>
>They left an intentional back door, however, which I managed to find: there
>is no bounds checking on PDL(). :-)

True, you could do a PDL(29) to access $C081 to disable the
language card.

Another, much more subtle way of getting into the monitor with all
"useful" commands disabled, would be to use a line number in the
range 437760 - 440319 with LIST, GOTO, RUN, GOSUB or DEL! Due to
the way the LINGET routine is written (to save three bytes!) it
will work correctly most of the time, but with line numbers in the
above range it will crash!


Christer Ericson --- Internet: christer@cs.umu.se --- tel: +46-90-166794
Department of Computer Science, University of Umea, S-90187 UMEA, SWEDEN