Black magic
WordNet
noun
(1) The belief in magical spells that harness occult forces or evil spirits to produce unnatural effects in the world
WiktionaryText
Noun
- Magic derived from evil forces, as distinct from good or benign forces; or magic performed with the intention of doing harm.
Usage notes
When referring to advanced technology, calling something (plain) means that it is not understood, but implies that it can be by those versed in the field. , on the other hand, implies that few understand it.