Most companies ban social networking while on the job, according to a survey from Robert Half Technology. More than half (54 percent) of chief information officers said their firms prohibit employees from visiting such social networking sites as Twitter, Facebook and MySpace while on the job.

The survey was based on interviews with more than 1,400 CIOs from U.S. companies with 100 or more employees.

“Using social networking sites may divert employees’ attention away from more pressing priorities, so it’s understandable that some companies limit access,” said Dave Willmer, executive director of Robert Half Technology.

But about one in five companies (19 percent) allow employees to surf the sites for work-related purposes, 16 percent allow it for limited personal use and 10 percent say it’s permitted for any type of personal use.