"As companies have designed browsers and plugins to be more secure over time, malware purveyors have also employed social engineering, where the malware author tries to deceive the user into installing malicious software without the need for any software vulnerabilities," Provos explained.

, for example, masquerade as legitimate security warnings even as they infect the user's computer with malware.

Socially engineered attacks are not yet as common as drive-by downloads, but they're "a fast-growing category likely due to improved browser security," Provos said.

Google Webmaster Tools

Google sends thousands of notifications every day to webmasters and Internet Service Providers, and its Safe Browsing effort currently helps to safeguard some 600 million users through built-in protection for , Firefox, and Safari.