Rogue Programs on Public Computers

Persons of a certain age may remember that LONG ago, in the age of the 8-bit home computer, many retail stores would have the machines on display. They were powered up and, well, not usually doing much; usually just sitting at a BASIC prompt awaiting some inquisitive 10 year old's efforts at programming.

Oh, and program we did.

My own forays into storefront coding amounted to little more than typing the following onto any Commodore machine:
1 PRINT "ZX Spectrums are skill"
2 GOTO 1
Not exactly mature or imaginative (and for the record, Commodores are also skill. And quite probably ace too). However, I received an email from a reader (and therefore man of wealth and taste), Eli. It said:

Well, firstly, thanks for sharing that and, secondly, it's an absolutely smashing little bit of BASIC. Try it out, folks, it's lovely.

Now all of this has got me thinking - what other little rogue store programs were out there? What kind of evil little things did your grubby young fingers rattle into that unattended Apple II? What uninterruptable bit of bleeping, colourful nonsense did you inflict on the nearest BBC Micro? Please share! All platforms are welcome. Please sling them in the comments below.

30 years back, I used to put this little proggie up in W.H.Smiths on their Spectrum computers, then booby-trap it so passing school-kids couldn't list it... Yes, I was that evil..

It creates a 'Moire interference pattern' on-screen, then wipes it on the next pass... looks like a radar display making a snowflake pattern, then erasing it...

I might have slightly forgotten the last bit.. 59^3*PI, it might be 52... or 57... guess the old RAM is fading with age...