The program exploited a buffer overflow bug in Microsoft's SQL Server and Desktop Engine database products.
The slowdown was caused by the collapse of numerous routers under the burden of extremely high bombardment traffic from infected servers.
The flood of routing table update notices caused some additional routers to fail, compounding the problem.
Eventually the crashed routers' maintainers restarted them, causing them to announce their status, leading to another wave of routing table updates.
Soon a significant portion of Internet bandwidth was consumed by routers communicating with each other to update their routing tables, and ordinary data traffic slowed or in some cases stopped altogether.