Stay informed with free updatesSimply sign up to the Cryptocurrencies myFT Digest -- delivered directly to your inbox.Crypto investors worried about their tokens getting hacked are boosting demand for secure devices and wallets that keep customers’ tokens safely offline.As hack attacks on companies and individuals have hit a record, Ledger, which sells hardware devices resembling USB drives that help investors securely store their cryptocurrencies, said it was having its best year yet.Pascal Gau...