Malware that exposed credit card or banking information represented 74 percent of the top 50 malicious code samples reported to Symantec in the first half of 2005, up from 54 percent in the previous six months.
The company, which released its semi-annual internet security threat report Monday, said the increase in confidential information threats is likely due to the rapid growth of bots - compromised systems that are hijacked by attackers to send spam or denial-of-service attacks.
In the first six months of this year, Symantec counted an average of 10,352 bots per day, up from less than 5,000 a day last December. The increase in bot activity has driven a corresponding increase in DoS attacks from 119 to 927 per day, according to the company.
"The new threat landscape will likely be dominated by emerging threats such as bot networks, customizable modular malicious code, and targeted ttacks on web applications and web browsers," researchers wrote in the report.
Online criminals today are motivited by profit, rather than curiosity or interest in showing off technical skill, they said.
In the first half of 2005, Symantec documented more than 10,866 new Win32 viruses and worms, an increase of 48 percent over the 7,360 in the second half of last year. The company said the increase signifies a shift away from broad threats such as mass-mailing worms and towards modular and customizable malware.
According to Symantec, Mozilla browsers had the most confirmed vulnerabilities of any browser in the first half of the year with 25, 18 of which were rated as high severity. During the same period, 13 vendor confirmed vulnerabilites were disclosed for Microsoft Explorer, eight of which were high severity.