1. A system for processing email to detect the spread of previously unknown viruses which comprises: a computing system programmed for: monitoring email traffic passing through one or more nodes of a network, this monitoring comprising: analyzing emails to determine if they meet one or more predefined criteria, the predefined criteria indicating whether it is possible that a given email contains a virus, the predefined criteria including at least one of the given email having an attachment that is executable by the computing system, the given email having an executable attachment that is wrapped in a container, the given email containing an attachment having illegal formatting; logging details about emails that meet one or more of the predefined criteria to a local database, the details at least including at least two of the message digest of the subject of each logged email, a message digest of the message of each logged email if such a message was included with the email, a message digest of an attachment to the email if such an attachment was included with the email, and a message digest of the sender of each logged email, and the number of intended recipients of the email; assigning a suspiciousness score to each of the emails within the database that thus meet one or more of the predefined criteria, the suspiciousness score for each email relating to a degree of suspiciousness of a particular email according to one or more suspiciousness criteria the particular email meets, the suspiciousness criteria being different than the predefined criteria, the suspiciousness score being calculated using an algorithm which takes into account how similar the emails are to other emails in the database, and how many such similar emails have been received during a predefined length of time of 180 minutes or less, the suspiciousness score increasing as the number of similar emails received increases over the predefined length of time; searching the local database for patterns of recent email traffic which are indicative of, or suggestive of, the spread of a previously unknown email-borne virus, by applying a predetermined set of pattern criteria to attributes of the recent email traffic, the set of pattern criteria including criteria which relate to a plurality of constituent parts of recently arrived emails making up at least a portion of the recent email traffic, the recently arrived emails being emails that have arrived during the predefined length of time; detecting the suspected presence of a previously unknown email virus based on a detected pattern of email traffic which is indicative of, or suggestive of, the spread of a previously unknown email-borne virus; and, initiating, once such a pattern is detected which meets predefined threshold criteria, a remedial action, wherein the remedial action is selected from among an automatic remedial action, alerting an operator and both an automatic remedial action and alerting an operator, the remedial action being at least partly determined by the degree of suspiciousness associated with the detected pattern of email traffic.