Research reveals that the majority of "malicious" websites are now legitimate sites that have been compromised by attackers.
The Websense Security Labs report says the number of legitimate websites compromised by attackers has surpassed those purposefully created by attackers.
Attackers know that compromising sites with generally good reputations can increase the success rate of attacks, said Websense.
For instance, last year, Websense discovered an attack launched within the United Nations' HIV/AIDS Asia Pacific portal.
In this case, when visitors opened the United Nations website, unprotected users inadvertently downloaded a Trojan horse that infected their computers with malicious code.
Victims became unknowing participants in a larger bot network that attackers could use for future malicious attacks, posing a risk to both personal computer users and businesses.
Last September, Websense says it was first to find the Web 2.0-based "Phast Phlux Phishing" attack on the social networking site MySpace.
After MySpace announced increased measures to protect users from online threats, many users were compromised by this scam that stole confidential user login credentials for malicious purposes.