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The growth of malicious code slowed between July 2001 and the end of last year, but new viruses pose a more constant threat and last longer than those of previous years, a new survey of companies has found.

The Virus Prevalence Survey was conducted by ICSA Labs, an independent division of security firm TruSecure. ICSA Labs gathered information from 306 medium-size and large companies and from government agencies. The purpose of the survey was to understand trends in the prevalence of viruses and malicious code on computer networks. It covered more than 900,000 computer desktops, servers, and gateways, according to TruSecure.

Infections Increase

More than 1.2 million incidents involving viruses or malicious code were recorded during the course of the survey, which translates to 113 virus encounters a month for every 1000 machines on a network during the 18 months covered by the survey.

The pace of infections has grown at a rate of about 12 virus encounters per 1000 machines each year since the survey began in 1996. However, between 2001 and 2002, that growth was considerably slower than in previous years, increasing by only 2 encounters per 1000 machines, the survey found.

ICSA Labs also noted a decrease in the number of companies reporting a virus "disaster" during the survey period. Of respondents, 80 percent said they had experienced a virus disaster, down from 84 percent in ICSA Labs' last Virus Prevalance survey. ICSA Labs attributed that decrease, in part, to the absence of a massive virus outbreak along the lines of the Code Red or Klez viruses in previous years.

Viruses were a more constant threat in the survey period than in previous years. The average rate of infections per month was higher than in previous years, and the threat of incidents remained at a higher level throughout the period covered by the survey, ICSA Labs said.

Despite the slowdown in the growth of new viruses and the absence of a Code Red-style outbreak, the viruses that did circulate appeared to have more staying power than those in previous years, according to ICSA Labs.

The prevalence of mass-mailing viruses and Internet worms accounts for the increase in durability; those virus types are harder to remove, even after virus definitions are available.

As a result, new variants of the Klez worm linger on networks, rather than spiking shortly after they are introduced and then quickly dying out, ICSA Labs said.

Pay Now or Later

The cost of cleaning up after a virus infection also rose in the survey period. On average, 23 staff days were required for virus disaster recovery, up from 20 days in ICSA's last Virus Prevalence survey. The average cost to companies was $81,000 for companies responding to the latest survey compared with $69,000 in the last survey, ICSA Labs said.

The world may just be witnessing the transition from an older generation of viruses and worms to a new one. New virus types, expanded connectivity, and the spread of wireless devices mean that infection rates will likely grow in the future, ICSA Labs said.

To protect themselves, corporations should adopt holistic protection philosophies that supplement antivirus technology with e-mail gateway filtering and controls on desktop applications and Web browsers.

Complementing identity-based antivirus screening with more flexible heuristic antivirus technology will also help defend against the next generation of Internet viruses, ICSA Labs said.

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