This alarming figure is revealed in the 2006 Australian Computer Emergency Response Team (AusCert) Computer Crime Survey in a survey which drew responses from almost 400 companies in Australia.

For the first time, AusCert has segregated the category of "virus, worm or trojan infection" into two specific categories, virus or worm infection and trojan or rootkit infection. As a result, the survey found 21 percent of respondent companies' networks were hit by a rootkit while 45 percent had experienced a virus or worm

AusCert general manager Graham Ingram says the figure for rootkit infection is "disproportionately high".

Ingram said that in the past, enterprises viewed trojan and rootkit infection as a home PC issue.

Malicious code sidesteps detection