For the second time in less than 18 months, the job-search Web site Monster.com was breached, along with USAJobs.gov, which Monster’s parent company runs for the federal government. And yet Monster might suffer little fallout — because the overall state of computer security is so bad anyway. Attacks against Web sites have become so common, security experts say, that Monster Worldwide won’t necessarily scare customers away with its January disclosure that its database was plundered of user IDs, passwords, email addresses, names and phone numbers.