Yesterday, security firm Hold Security revealed that 1.2 billion email addresses had been stolen by Russian hackers. Security expert Brian Krebs has responded to the news by posting answers to questions on his blog. In the post, he reveals that major spammers rely on lists of billions of email addresses in order to distribute malware. Should email users be concerned? "If you are the type of person who re-uses passwords at multiple sites — including email accounts — then the answer is yes," he writes. "If you re-use your email password at another site and that other site gets hacked, there is an excellent chance that cyber crooks are plundering your inbox and using it to spam your friends and family to spread malware and to perpetuate the cybercrime food chain."