Collection #1 is a massive credential-stuffing compilation built from thousands of earlier breaches. leaksear.ch indexes 2.69B records containing email addresses with plaintext or hashed passwords, creating risk for anyone who reused credentials.
A Bell Canada 2017 breach dataset indexed by leaksear.ch contains about 3.4 million records from an internal WEB_USERS table. Public reporting at the time confirmed illegal access to customer emails, names and phone numbers, while the indexed dataset also includes usernames, IP addresses, passwords or passcodes and survey data.