McAfee Avert Labs described the assault as "one of the largest attacks to date of this kind".
The attack serves as a reminder that even trusted websites can be malicious, McAfee warned.
"Often you hear warnings about not going to untrusted sites," said Craig Schmugar, threat researcher at McAfee Avert Labs."That is good advice, but it is not enough."
McAfee Avert Labs first spotted the attack on 12 March.
I wonder who can sell us some sort of software to guide us out of this maze of evil webpages?