^As Geordi's little virus idea in "I Borg" was never actually tested, there's no way to know whether it would have been completely effectively, partially effective, or in fact completely useless.
Assuming that it would work...well, you know what they say about assumptions...
Borg #1: "What's this?"
Borg #2: "It's a shape."
Borg #1: "But it's a paradox, that shape can't exist in nature."
Borg #2: "You're right... Deleted as irrelevant."
Borg #1: "Cool. Wanna go assimilate some stuff?"