The 2008 edition of Cisco's Annual Security Report found that the overall number of disclosed vulnerabilities grew by 11.5% over 2007. Vulnerabilities in virtualization technology nearly tripled from 35 to103 year over year, and attacks are becoming increasingly blended, cross-vector and targeted.

Cisco says its researchers saw a 90% growth in threats originating from legitimate domains, nearly double what was seen in 2007. And the volume of successfully propagated via e-mail attachments is declining -- over the past two years, the number of attachment-based attacks decreased by 50% from 2005 and 2006.

This is at least the fourth study on security released this year by Cisco. Three other, conducted by an external research firm but commissioned by Cisco, assessed ,  and .

According to Cisco, spam accounts for nearly 200 billion messages each day, approximately 90% of worldwide e-mail. The United States is the biggest source at 17.2%, ahead of Turkey (9.2%), Russia (8%), Canada (4.7%), Brazil (4.1%), India (3.5%), Poland (3.4%), South Korea (3.3%), and Germany and the United Kingdom (2.9% each).

More online attackers are using real e-mail accounts with legitimate Web mail providers to send spam, which makes it harder to detect and block, Cisco says. The company estimates that in 2008 spam resulting from e-mail reputation hijacking of the top three Web mail providers accounted for less than 1% of all spam worldwide but made up 7.6% of the providers' mail traffic.