Internet service provider America Online reported Thursday that it has blocked nearly half a billion virus-infected e-mails from reaching its members since launching, in mid-April, automated e-mail attachment screening. The company estimates that its virus-screening system, based on security software maker Network Associates' technology, shielded each of its 32 million members from an average of 15 different virus attacks.
AOL said it is blocking almost 1 million virus-laden e-mails each day, with the single largest wave of infected messages arriving during the height of the Sobig.F worm outbreak, when the company intercepted 24 million contaminated e-mails in a 24-hour period. Sobig.F also proved to be the most persistent virus AOL has encountered, as it was present in nearly 350 million of the 500 million messages the ISP has blocked thus far. The five most prevalent viruses AOL has battled are, , , and .