Yahoo revealed that it an intrusion into its network in late 2014 had given hackers access to 500 million users’ usernames, email addresses, phone numbers, dates of birth, passwords, and a mix of encrypted and plaintext security questions and answers. The company’s CIO claimed the attack was perpetrated by a state-sponsored actor.
No
A cyber attack is a cyber operation, whether offensive or defensive, that is reasonably expected to cause injury or death to persons or damage or destruction to objects.
Michael Schmitt et al; Tallinn Manual 1.0, pp 92
- ✅ Cyber Operation?
- ❌ Expected to cause death or injury to people or damage to objects?
Russian Intrusion of Yahoo does not match this definition. Here's a list of actual cyberattacks and and why this matters.