Small businesses wrongly believe that they're too insignificant to attract hackers and spend too little time on security. That's according to the latest survey from security vendor McAfee which found that many SMBs thought they were immune from theft.

"Lots of small attacks add up to large amounts of revenue," said McAfee, , which polled 500 companies in the U.S. and Canada. There are an estimated 7.4 million SMBs in North America.

McAfee's study this year focused on North America, whereas last year it surveyed 600 European SMBs. However, the conclusions of the two studies are similar.

About 45 percent of North American businesses felt they did not have valuable data to steal. Last year, 58 percent of European businesses gave the same response.

Part of the problem is that attention to security takes time, and SMBs have fewer resources. Many don't have an employee dedicated full-time to IT security. But McAfee argues that SMBs could face critical shutdowns in business as a result of weak security.

Every business retains employee data, which could be valuable, the survey said. Also, every business is hit with spam, which often is laden with malicious data-stealing programs.

McAfee said it expects hackers to increasingly go after VoIP phone systems, virtual systems as well as mobile devices. McAfee's advice: patch regularly, filter email and use anti-virus software.