Collection #1 is a 2019 mega-dump of 773 million email/password pairs aggregated from thousands of breaches — it's now a standard wordlist for credential stuffing.

The leak:

• Released January 2019 on hacking forums
• ~87 GB of data, 12,000+ separate breach files merged
• 773 million unique emails
• 21 million unique plaintext passwords

What makes it special:

• Many passwords were cracked before publication — published as plaintext, not hashes
• Aggregates breaches over years — your 2014 forum password is in there if it was reused
• Followed by Collection #2-5 (~2.2 billion total credentials)

How attackers use it:

1. Credential stuffing — feed the email/password pairs into login forms on every major service (banks, email, gaming, e-commerce)
2. Wordlist for new attacks — feed the 21M unique passwords into Hashcat to crack new breaches
3. Phishing target lists — emails are sorted, valid → spear-phish at scale

Why it's still dangerous in 2026:

• People rarely change passwords proactively
• Many sites still don't enforce breach checks
• Even if YOU rotated, your old password reveals patterns ("Spring2018!" → likely "Winter2024!" now)

Self-defense:

• Check yourself: https://haveibeenpwned.com/ (HIBP)
• Use a password manager → unique password per site means breaches stay isolated
• Sign up for breach notifications

The bigger picture:

The Cambridge Cybercrime Centre estimates that aggregated leaked credentials power billions of credential stuffing attempts daily. It's the most common form of attack on online services.

Wikipedia: https://en.wikipedia.org/wiki/Collection_No._1.

Go deeper:

• Collection #1 (Wikipedia) — 773M emails / 21M plaintext passwords aggregated from 2000+ breaches.
• Troy Hunt: Collection #1 Data Breach — first-hand HIBP writeup on its credential-stuffing significance.

ICMPv6 is the redesigned control/error-message protocol for IPv6; beyond classic error messages it adds "Packet Too Big" and absorbs multicast group management and Neighbor Discovery.

ICMP in IPv4 mostly did errors and ping. ICMPv6 is far more central to how IPv6 works:

• New/important message type: "Packet Too Big" — the backbone of Path MTU Discovery (since routers no longer fragment)
• Multicast group functions (the role IGMP played in IPv4) are folded into ICMPv6
• Neighbor Discovery Protocol (Router/Neighbor Solicitation & Advertisement) — the replacement for ARP — is built on ICMPv6 messages

Because so much depends on it, blocking all ICMPv6 at a firewall breaks IPv6 (unlike IPv4, where you can often filter ICMP fairly aggressively).

Tip: ICMPv6 uses Next Header value 58. Don't firewall it blindly — Neighbor Discovery and PMTUD will stop working.

Go deeper:

• ICMPv6 (Wikipedia) — the message-type table, including "Packet Too Big" and the NDP messages that ride on ICMPv6.