Despite Apple's best efforts, unsavory labor practices are still being used to build iPhones, iPads, and Macs. In its ninth annual report on supplier responsibility, the company says it's auditing more factories than ever, reimbursing unpaid workers, and tackling violations "proactively." However, the sheer scale of Apple's supply chain and its need for seasonal labor means that meaningful oversight is a difficult goal.

For example, although the latest report covers some 1.6 million workers, even this admirably large catchment leaves hundreds of thousands of individuals' working conditions unexamined. (The upper limit of how many people Apple indirectly employs is hazy, but the company itself says it educated at least 2.3 million workers on their rights and Apple's code of conduct in 2014.) The graph below shows how difficult it will be for Apple to ever stamp out labor violations entirely, with the number of facilities employing underage workers or using bonded labor fluctuating back and forth. This last form of labor violation is relatively unheard of in the West but is classed by the UN as a form of slavery. Foreign or migrant workers are told that they need to pay "recruitment fees" to secure a job, meaning they're in debt to their suppliers before they've even begun working. Often workers' passports are then confiscated to keep them compliant.

However, this data is only part of the picture. For a start, the actual number of child laborers per facility can be relatively low. In 2014, for example, there were 16 individual cases at six facilities (0.001 percent of the workforce) with Apple reporting that it "successfully remediated" all of them. (This means that the supplier has to pay for the child's education while still paying them wages and offer them a job again when they come of age.)

Although in terms of bonded labor the numbers are much higher, Apple forces suppliers to directly reimburse them, paying out $3.96 million in 2014 to over 4,500 foreign contractors. As with a lot of this data it's hard to know exactly how to react. On one hand, this type of openness exposes a practice that can now be fixed, but on the other, this report shows that at least four and a half thousand known individuals — likely more — were essentially working as slaves last year just to make the Apple products that so many of us buy.

And in other metrics it's clear that Apple is making a concrete difference. A few years ago, factories forcing employees to work more than 60 hours a week were a major problem for Apple, with 62 percent of the facilities surveyed violating this limit. Now, in the latest report, just 7 percent of audited facilities were exceeding the 60-hour mark — and that comes from a far larger sample size. The company took the decision this year to also ban bonded labor altogether (it previously drew the line at "recruitment fees" in excess of one month's pay). To date, the company says it has also "terminated relationships" with 18 suppliers over repeat violations.

For Apple, however, this is a game of whack-a-mole that no other company even attempts with such transparency. The iPhone maker continues to deliver record sales and the global demand for smartphones continues to grow. Apple's employee headcount isn't likely to dip anytime soon (at least until those robot factories get going) and for the moment the best thing it can do is stay vigilant.