I know Lamer Exterminator very well.
But Lamer came in two main types: the one made a random block UNUSABLE by filling it with LAMER!LAMER!LAMER!...
As far as I remember, the block data previously contained in it was irreparably lost
(unless it was an unused block, lucky you!).
The other type altered the boot-code: it changed the disk from bootable to non-bootable, making the WB hand show up at the start. If you installed a fresh AmigaDOS bootblock on it, it booted again.
Well, sorta stupid virus it is, undoubtedly.
But I do NOT think this has something to do with copy-protection. I repeat again: the checksum IS CORRECT, the error happens because block #11 (for example) has a pointer
to the next block, which is block #2 in this example! And as you know, if the data block chain (example: 11 - 2
- 3 - 4) gets broken up
by an NON-DATA block (00000000, thus treated as "unreadable" [in this case block #2
]!), AmigaDOS spits out a checksum error.
And I say it again, just change the 00000000 to 00000008 and the disk works again. without having to modify ANYTHING ELSE (including the checksum).
I assume from the investigation done that it does stuff up the games so they don't load
Exactly. And they load again if you "repair" the block by giving the "data block status" back to it. Well you cracked Gridiron back then, so just look at the uncracked disk image originally posted here. It's the same thing as with the disks I'm currently checking.
This is either a virus OR it was a means in the past by cracking groups to make disks unreadable for others (yes that's a verified true story, I did get some disks into my hands from a (former) group member that had an intentional checksum error on block #881 - all the Amigas of the group members were equipped with a PATCHED (!) kickstart ROM).