In the world of 'puter-geeks, there are hackers and defenders ..

[music] DUN DUN ... and this is a story about their battles:

To make a long story short, the most popular way to spread viruses nowadays is to hack a popular website and inject its webpages with viruses so when people visit that page, the virus is automatically downloaded to the victims' computers. This is called "drive-by downloading." Moderately popular websites like WXC are actually the prime candidate for this type of hacking because there is enough traffic but probably not a dedicated IT security staff.

Also, anti-virus programs cannot catch ALL viruses. There might be a virus that McAfee cannot catch that can be caught by Symantec or AVG, and vice-versa.