There may be a larger number of data breaches attributable to employee errors, but those caused by malware or spyware are most expensive, note survey findings released by San Francisco-based Beazley Insurances Services. Beazley Insurance – which analyzed 1,500 data breaches serviced by the company in 2013 and 2014 – reports the two most common sources of breaches were unintended disclosure, while breaches due to malware or spyware are, on average, 4.5 times more costly than unintended disclosure.