BYOD requires a significant portion of corporate IT resources dedicated to managing and maintaining a large number of devices within the organization. In the past, companies tried to limit business smartphone use to a single platform. This made it easier to keep track of fixes, because all employees were using the same devices, or at the very least, the same operating system. The most popular employer-issued smartphone used to be Research in Motion's BlackBerry,because it was considered the "most secure" mobile platform available.(BlackBerry mobile devices access corporate e-mail and data using a proprietary software and networking platform that is company-controlled and protected from outsiders.)