We operate both inbound and outbound firewalls across all of our shared hosting offerings. We also have IDS (intrusion detection systems) on both the servers and routers to capture/track/prevent malicious requests where possible. This is all coupled with high frequency software patching and restricted user level functionality.
As you can imagine ensuring the security of our servers reduces the possible likelyhood of things going wrong which inturn lowers our long-term overheads.