i think but am no expert...
supporting fire is about attacking to engage or destroy enemy, relieving our forces in maneuvers.
in context of hacking this would be most likely DOS/DDOS attacks at network nodes (computers etc), which pose possible/real threats; or 'turning off' computer systems more permanently, for example with scripts that install hacks then automatically turn off computers, or perhaps there are even hardware destroying hacks (i don't know), or other attack methods with such effects.
i do not know if it's true that it's heavy losses on both sides, but i imagine losses happen during such maneuvers.
see also: Device Formations, combat and communication strategy.