About 47 percent of all respondents had a worm infect a company network in the past year, the Mazu survey found. One-eighth of those businesses had more than 25 percent of their network compromised during the incident.
Even worse

Almost one-fourth of all companies had an internal breach in 2004, and 40 percent of those incidents interrupted a critical service. Almost half of the IT professionals surveyed found active accounts belonging to ex-employees and one-third found rogue wireless access points in their network.
A few years ago I don't think responses would have been this candid. I think it says a lot about society's attitude toward breaches when companies aren't afraid to admit it, even without there name attached.