Civil servants this month are marking three years since the initial roll-out of Phoenix, which resulted in more than half of all federal employees being overpaid, underpaid or not paid at all.

A newly released federal report estimates the problem-plagued Phoenix payroll system has already cost government coffers more than $1 billion and could require an additional $500 million a year until it is fixed.

The auditor general's second, more detailed report into what went wrong with the Phoenix system was released on Tuesday morning.