IDC surveyed more than 2,600 information workers and 550 IT administrators in nine countries and found that IT administrators aren't aware of how many people use their own devices at work and how extensively they use those devices to access corporate applications.

Eighty-seven percent of IT managers said workers get their smartphones and other mobile devices from the company, and that the company covers their costs. Yet more than half of employees with iPhones, Android phones and iPads said they bought the devices themselves, according to the survey.

"Enterprises think they are in control of these devices, but in fact they are in control of only a small part of their infrastructure, with a significant number of employees going off the grid in acquiring and using their own devices," IDC said.

The use of employee-purchased devices is up compared to last year. IDC found that 40.7 percent of devices, including PCs, smartphones and tablets, that people use to access business applications are owned by the workers. That's up from 30.7 percent last year. Nearly 10 percent of those surveyed this year said they use a personal tablet for work.

IT departments also seemed unaware that people are using devices like smartphones and tablets to access company applications. IT managers said they thought 34 percent of staff were using a smartphone to access business apps. But 69 percent of workers said they used smartphones, whether personal or corporate-owned, for business apps. Asked the same question about tablets, IT administrators said 6 percent of workers used tablets, but more than double that number--13 percent--of workers reported doing so.