POPFile was doing something incredibly simple (if enabled). Imagine there are two classes of email (ham and spam) (POPFile was actually built to do classification for arbitrary categories but often used as a spam filter). When a message was received and classified its classification was assumed to be correct and the entire message was fed into the training as if the user had specifically told the program to train on it (which was only done when messages were incorrectly classified).
In the two class case the two classes (ham and spam) were so distinct that this had the effect of causing parameters that were essentially uniquely associated with each class to become more and more important to that class. But also, it caused the filter to pick up new parameters that were specific to each class (e.g. as spammers changed their trickery to evade the filters they would learn the new tricks).
There was a threshold involved. I had a cut off score so that only when the classifier was fairly "certain" if the message was ham or spam would it re-train on the message.
POPFile was doing something incredibly simple (if enabled). Imagine there are two classes of email (ham and spam) (POPFile was actually built to do classification for arbitrary categories but often used as a spam filter). When a message was received and classified its classification was assumed to be correct and the entire message was fed into the training as if the user had specifically told the program to train on it (which was only done when messages were incorrectly classified).
In the two class case the two classes (ham and spam) were so distinct that this had the effect of causing parameters that were essentially uniquely associated with each class to become more and more important to that class. But also, it caused the filter to pick up new parameters that were specific to each class (e.g. as spammers changed their trickery to evade the filters they would learn the new tricks).
There was a threshold involved. I had a cut off score so that only when the classifier was fairly "certain" if the message was ham or spam would it re-train on the message.