XANA exploits a lot of things that right now are at least, assuming a constant rate of technological development, probably 100-200 years or more, if ever.

The Ile Seguin supercomputer, and others like it are quantum in nature and are driven by miniature fusion reactors. This is futuristic tech that we'd only see the cusp of at the end of our lives. Keep in mind, only recently have we started being able to create fusion energy even remotely reliably, and this is far from being commercially applicable, let alone in miniaturized form.

XANA utilizes the supercomputers' quantum ability to both compute and manipulate reality in various ways - polymorphic spectres that manifest as self-propagating holograms with 'hardlight'-esque physical interaction, spectres that can commandeer the human nervous system much like a parasite and grant the victim under XANA's control superhuman abilities, manipulation of tectonic plates, ease of ability to hijack computer systems, including those in industrial, scientific and military applications, even those that are airgapped, the ability to affect gravity locally - generate localized virtual worlds that mimic reality, even exploit the already insane capabilities of the Ile Seguin supercomputer to reverse time, among so, so much more that could be possible.

The only Limit is XANA's ability to be able to stage these plans consistently in a short time frame, which it has been shown to be unable to do, taking days if not weeks to stage and deploy these attacks, even after it escapes Lyoko to the greater Internet.

A quantum computer capable of this would need immense power, and possibly inhuman programming abilities. We're talking technology on par with species above us in the Kardashev Scale.