The typical Internet surfer reuses the same password at an average of 49 websites, says a password manager software maker. Hackers can crack a batch of passwords and use them to attack sensitive sites. LivingSocial had to reset the passwords of about 50 million users last week after it discovered those credentials had been compromised in a data breach. One way to blunt the impact of breaches like the one on LivingSocial would be for online services to adopt two-factor authentication, an expert says. “There’s always a push-pull between what’s mandated versus what’s convenient,” he said.”]