mamazeb

How easy is it to recover data from erased MDs? Or rather, how easy is it to prevent data recovery? I have access to a large collection of used minidiscs which were 'wiped' by their former owner. However, as they were used for confidential interviews, would the deletion or formating procedures provided on the minidisc recorder they were used with be sufficient to make data recovery very difficult? Or should they be put through a further process of data cleansing (short of physical destruction). Thanks for any help and apologies if this question is answered elsewhere.