Fifty-eight percent of the large companies surveyed said they had security concerns about open source, while the figure for small and midsized businesses was slightly higher, at about two-thirds. Within those groups, only 9 percent of enterprises said they were "very concerned," compared with 45 percent for the SMBs.

More than half of SMBs (57 percent) also expressed concern that open-source software would be complex and hard to adopt, but only 32 percent of enterprises expressed a similar sentiment. In addition, 68 percent of SMBs cited the availability of service and support for open-source software as a concern, compared with 47 percent of enterprises.

The findings are among a wide range of data Forrester collected for two reports, "The State of SMB Software: 2009" and "The State of Enterprise Software: 2009."

Meanwhile, security concerns over SaaS (software as a service) seem to be diminishing among companies large and small, according to Forrester.

The research firm polled a subset of SMB respondents who indicated they weren't interested in SaaS. Twenty-seven percent named security as a factor, compared to 57 percent in a 2007 survey. A similar poll of enterprises saw 31 percent cite security concerns with SaaS, down from 47 percent in an earlier study.