In particular, only 36 percent of over 600 IT practitioners at large companies said that their companies were able to restrict the sharing of confidential documents with third parties, and only 27 percent were able to restrict sharing between employees.
"A lot of people focus on regulatory compliance, like personally identifiable information or PCI," said Ron Arden, COO at data security vendor Fasoo, which sponsored the study. PCI DSS, the Payment Card Industry Data Security Standard, spells out how companies must protect credit card data.
Plus, the loss of confidential data doesn't usually make the news headlines, he added.
Most companies don't keep track of where their most sensitive documents are moved to.
For example, according to the survey, 58 percent of companies say their employees use free, consumer-grade online file sharing applications, and 48 percent say that there are situations when it is acceptable for employees to keep confidential documents on their home computers or personal mobile devices.
In addition, 68 percent said they don't even know where their confidential information is located.
"A lot of people don't realize how much intellectual property or trade secrets is floating around the organization," said Arden.
The study also reported that 56 percent of respondents said their companies did not educate their employees about protecting confidential information, and only 44 percent of respondents said their companies used data loss prevention tools.
Other techniques for protecting documents include attaching protection technology to the documents, or by storing the documents in a centrally accessible, password-protected location. Fasoo, for example, protects documents with a small app that sits on user computer and mobile devices that allows them to open secured documents in their native applications, such as Microsoft Word or Adobe Reader. For those who don't have the app, such as external recipients, the document opens in the browser, and users need to log in to access it.
Another reason why companies aren't aggressive about protecting their confidential documents is that it can be hard to get funding, said Arden.
"The CIOs would go to the board to get funding to plug the leaks, the board asks if there was a leak last year, the CIO says no, and they don't fund it," he said.
Of course, companies often don't even know when proprietary documents are stolen.
But while only 23 percent of companies conducted an audit of their confidential documents, of those who did, 69 percent say they found security issues that needed to be addressed, according to the survey, which was conducted by the Ponemon Institute.
When losses were discovered, careless employees were the primary cause 56 percent of the time. The next most common cause, at 37 percent, was lost or stolen devices, followed by third party mistakes at 35 percent. Outside attackers were responsible for only 22 percent of breaches. Respondents were able to select multiple answers.
This is very different from the latest Verizon Data Breach Investigations report, which showed that more than 80 percent of all breaches were due to malicious outsiders.
However, the Ponemon study focuses specifically on the loss of high-value company documents, rather than more general breaches, such as stolen credit card numbers. In addition, the Verizon report is based on reports from police and forensics investigators who are most likely to be called in for a breach by outsiders.
"When it's internal, that kind of data breach is not necessarily one where you would contact the FBI," said Larry Ponemon, chairman and founder at Ponemon Institute.
In addition, while regulators require companies to report the loss of personally identifiable information, that typically doesn't apply to sensitive internal documents such as financial reports or trade secrets.
"We know that a lot of data breaches don't get disclosed," Ponemon said.