DJL Software (for "Dave J and John LookerSoftware") is mainly known as the co-author of the [[Speedlock|Speedlock]] protection system, a fastloader used on many cassette games released in the UK, but he was also the author of several Amstrad games including 3d Stunt Rider and Nigel Mansell's Grand Prix.
Speedlock was a modified version of the [[Spectrum|Spectrum]]'s A fast loader and protection used on many cassette routines with games, and as a protection addedon disc games.
As DJL was also the protection system continued to evolve, programs such as author of several Amstrad games including [[Soft-Lok|Soft-Lok3d Stunt Rider]] and the [[Bonzo|BonzoNigel Mansell's Grand Prix]] suite were upgraded , in addition to break the protectionself-published titles such as [[https://www.retrogames.co.uk/041976/Sinclair/Frogger-by-DJL-Software Frogger]].
A separate disc protection system, [[8k Speedlock|8k Speedlock]], relied on the fact that the Category:CPC's hardware could reliably read but not write 8k sectors. To get around this, the [[Executioner|Executioner]]'s utility [[Xexor|Xexorscene members]] included a 'brain file' solution to crack individual games before copying them.