Several Web administrators from major companies said their Windows-based Web servers were compromised despite being up to date on security patches, security analysts reported.
"We've been watching activity since last Sunday, but it's now hit a critical mass," says Marcus Sachs, director of the SANS Internet Storm Center, who is in communications with Homeland Security's National Cyber Security division about the attack.
The attack appears to be one of the most sophisticated Internet attacks to date. The attackers are compromising and infecting E-commerce and corporate Web sites with malicious code. That code is used to infect Web surfers' using certain versions of Internet Explorer.
Security experts say Web surfers visiting these sites are at risk of having their machines infected with Trojan horse applications, used to hijack computers, as well as keystroke loggers, which are capable of stealing personal information such as financial account numbers and passwords.