A significant portion of spyware is designed specifically to steal identities, underscoring the trend toward more malicious use of such software by criminals, said a security firm Wednesday.

Fifteen percent of the 2,000 known spyware threats analyzed by Aladdin Knowledge Systems over a two-month span send private information gathered from the infected PC by logging keystrokes, capturing usernames and passwords, and hijacking e-mail address and contact lists.

About one-in-six pieces of spyware -- a category that also includes adware -- is "specifically designed for identity theft," said Aladdin in a statement.

Another 25 percent of the spyware examined gathers information non-identity information, but was classified by Aladdin as a "moderate threat" because these programs collect such data as the victim PC's operating system, domain name, process logs, security applications, IP address, and security updates installed.

The remaining 60 percent, said Aladdin, gathered "commercial-value information about the end user's browsing habits," the traditional definition of the often noxious but rarely dangerous adware.