Roughly half of all sexual impropriety reported in U.S. prisons and jails last year was perpetrated by correctional staff, not inmates. Female staff were the offenders in two-thirds of the prison cases, and two-thirds of the victims of prison staff were male inmates, according to the U.S. Bureau of Justice Statistics.

With 2 million men and 200,000 women behind bars in the United States, the problem appears small -- there were 344 substantiated incidents of staff sexual misconduct and harassment reported by authorities last year. But experts believe incidents are underreported, and the bureau study notes that many allegations remain under investigation.

Critics say just one improper relationship between staff and an inmate erodes discipline, security and morale in institutions where there is little privacy, few secrets and a strong reluctance to "snitch.

....While there is an element of supposed romance noted in many of the cases, sexual relations of any kind between prison employees and inmates are considered nonconsensual by law because of the inherent power that staff have over prisoners. In Virginia it is a felony punishable by up to five years in prison.

Smith said it is not surprising that a larger number of female staff in prisons are involved in sex offenses. Male inmates outnumber female inmates more than 10-to-1. The federal report did not break down the data for homosexual versus heterosexual misconduct, but assuming most staff and most inmates are heterosexual, you would expect to find more female staff reported as perpetrators and more male inmates as victims, she said.

"You will often find that the culture that allows this kind of stuff to happen is also a culture that is particularly inhospitable to female staff," she said, noting that female staff might align themselves with inmates for protection.