Infection through JavaScript! 
Those who are fans of Super Bowl, you will know that their web host
was hacked a few days ago.
Besides being hacked, the attackers also added in a malicious
JavaScript, which will download a backdoor trojan into your
computer.
From SC Magazine:
Dozens of unrelated websites contain malicious scripts that attempt
to infect users' machines with malware, security experts said
today.
The reports come two days after the highly trafficked website for
Dolphin Stadium, host of today's Super Bowl, was infected with a
JavaScript-enabled keylogging trojan that took advantage of two
previously patched Microsoft vulnerabilities.
In a blog post today, Marcus Sachs, director of the SANS Internet
Storm Center, listed about 50 sites that contain the malicious
pointers.
He urged system administrators to block network traffic to the
sites until it can be confirmed they are free of malware. Users can
be infected simply by visiting the websites.
Mikko Hypponen, chief research officer at F-Secure, said some of
the hacked sites relate to the Super Bowl.
Sachs, meanwhile, reported that a number of attacks are targeting
hospital or medical care sites.
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Disabling JavaScript is the only remedy. I see no other ways.