Denial of Service by massive network load.
Poisoning DNS or taking DNS down will prevent legitimate players from communicating with each other.
Using program flaw or exception to trigger excessive resource consumption (spinning process, writing all logs full, and leaking memory) or to cause a service to crash.
Feeding service request pattern (e.g. monotonically increasing input size so that previously freed memory is never enough to satisfy the new request) that causes fragmentation of memory, excessive or ineffective garbage collects, or memory leaks.