The growing risk of defects from increasingly complex in-house software is costing companies dearly, according to new research from IDC.

Seven in 10 companies said their code base is more complex than in the last two years, and 72 percent said debugging software was "problematic". The cost of fixing this costs medium to large firms on average between $5 million and $22 million (£2.5 million and £11 million) every year, IDC estimates.

In-house software is becoming more complex as a result of multicore processing, Web 2.0 and service oriented architectures (SOA), IDC said, and the complexity is also driving up the original costs of development.

There is such complexity in in-house software that reviews of code are not identifying some problems, IDC warned. A worrying one quarter of firms experienced regular, serious problems with software after reviewing code. And 41 percent found up to 10 critical defects, requiring patches, in the twelve months after software went into production.

This could be an expensive problem, IDC said. In one example, it estimated a software developer would cost $2,000 (£1,000) over 30 hours to repair a software defect. Most defects can take up to five days to fix, according to the research.

IDC interviewed 139 corporate development firms for the 'Improving Software Quality to Drive Business Agility' survey, which was commissioned by software quality measurement supplier Coverity.

The survey respondents described security, quality, code integrity, and business relevance as the most important factors on which to focus for software development. Security, customer-facing software, desktop, and transaction processing applications are updated at least daily by around a quarter of respondents.

"The increased complexity of software development environments and the cost of fixing defects in the field (rather than early in the software lifecycle) combine in exorbitant ways to drain income and to hamstring businesses as a result of critical software downtime," said Melinda-Carol Ballou, program director of application lifecycle management at IDC, and author of the report.

"Even as organizations understand greater complexity levels and acknowledge significant labor to repair software problems, they tend to underestimate current and ongoing costs for defect repair and business impact," she said. "This level of optimism can mask the need to evaluate and rework existing quality approaches."

The use of best practices, an assessment of automated testing technology, as well as a consideration for process and organizational change, would help businesses improve testing and development, she said. It is important, she said, that businesses understand the long term costs of poor quality software development, and invest properly early in the development cycle.