With no paper stock certificates, what guarantees that an investor can get his money if there is catastrophe?

Given that brokerages no longer mail paper stock certificates to investors, how can someone who owns stock be sure they will get their funds out of the market in a calamity (i.e., a computer virus that wipes out all computers/brokerage records)? Although there are insurances for stocks, do the brokerages keep paper records for each client? I have heard of some type of account ("clean....account") that can protect against this risk. What is the answer?