A spam filter is a software app that is installed on a POP3/IMAP server and keeps track of all incoming email messages in order to hinder any unsolicited ones from reaching a given mailbox. Several instances of such emails would be: offers for pills or money, false bank notices or attachments that contain malicious software sent with the idea of infecting your computer. Email filters typically check the content of an email and when they come across some keywords or other suspicious content, they either erase the email message or redirect it to the Junk/Spam folder instead of the Inbox folder. Certain web hosting companies combine their own spam filters with up-to-the-minute databases from spam-tracking organizations, so as to ensure higher levels of security for their clients. Such databases contain patterns, mail server IPs and other information about spam messages recently detected by these organizations.