Before spell scrolls were introduced, players were required to research each spell using different spell component combinations using a special Spell Research Panel. Some combinations would cast harmful self spells. After the research panel was removed it was no longer possible to learn these harmful self spells. However those players that had already learned them still have them in their spell books and can cast them to this day.
On the Spell List pages these spells are listed with a red X scroll icon indicating their retired status.