Tesco has warned its loyalty program members of a security incident that may have affected over 600,000 Clubcard holders. The supermarket chain believes fraudulent activity in customers accounts was possible due to older data breaches and leaks. The most popular strategy for reward program fraud is credential stuffing, meaning that the attacker inputs user credentials exposed in previous breaches. Loyalty program fraud has increased by 89% over the last year, with total losses estimated at $1 billion. The next time you sign up for a new loyalty program, avoid re-using an old or existing password.”]