Patent Application
20050204159
The invention relates generally to computer systems, and deals more particularly with a technique to effectively block spam.
The Internet is well known today, and comprises a network of user computers and servers. One role of the Internet is to provide a vehicle to exchange e-mail. A common problem today is “spam”, where a server sends commercial e-mails to numerous (thousands, even millions of) user computers via the Internet. The spam clogs the Internet and the mail boxes of the user computers, and wastes user time in identifying the spam and deleting it. Spam detectors and filters are well known today such as “Spam Assasin” (trademark of ______) program. Typically, a spam detector and filter are installed at an edge router or a firewall for a server. The server provides an e-mail transfer function for multiple user computers. The spam detector reviews incoming e-mail to detect when the same e-mail (i.e. same or substantially the same text) is addressed to multiple different users. The spam detector may ignore e-mails sent from entities known to be bona fide correspondents, such as employees of the same corporation to which the e-mails are sent. These entities can be recorded on a list accessible to the spam detector. But, the same e-mails sent from another entity to multiple different users are assumed to be spam. For those cases where the e-mails are assumed to be spam, the spam detector reads the IP address of the sender, and then blocks subsequent e-mails from the same IP address by creating a spam filter rule. Each spam filter rule may specify a source IP address from which e-mail will not be accepted. The filter rule is enforced at the firewall or router, or the gateway server in the absence of a firewall or router. The blockage or filter rule may be in effect for a predetermined amount of time, or can be periodically removed when there filter becomes too complex.
The problem with the foregoing spam blocking technique is that the “spammers”, i.e. the servers sending the spam, learn when their e-mails are being blocked. They can learn this by observing the TCP response to each of their e-mails. In the case of an e-mail being blocked, there will not be any acknowledgment. When their e-mails are being blocked, the spammers use a different server with a different IP address or a different IP address from the same server to send the spam. This will defeat the spam filter for a time until the spam filter identifies this new IP address as that of a spammer, and then blocks subsequent e-mails from this new IP address with a new filter rule. The foregoing iterative process can continue indefinitely, with the result that the spammer succeeds in getting a large amount of spam past the spam filter (between generation of the appropriate filter rules).
An object of the present invention is to improve spam detection and blocking.
The invention resides in a system, method and program product for blocking unwanted e-mails. An e-mail is identified as unwanted. A source IP address of the unwanted e-mail is determined. Other source IP addresses owned or registered by an owner or registrant of the source IP address of the unwanted e-mail are determined. Subsequent e-mails from the source IP address and the other IP addresses are blocked. This will thwart a spammer who shifts to a new source IP address when its spam is blocked from one source IP address.
According to features of the present invention, the other source IP addresses owned or registered by an owner or registrant of the source IP address of the unwanted e-mail are determined by first determining an owner or registrant of the source IP address of the unwanted e-mail. The owner or registrant of the source IP address of the unwanted e-mail and the other IP addresses owned or registered by this owner or registrant are determined by querying an entity that manages registration of IP addresses. This entity may be the Internet Assigned Number Authority. An email can be identified as unwanted when it has the same text or subject line as other e-mails sent from the same source IP address.
FIGS. 2(A) and 2(B) form a flow chart of a spam detection and blocking within the computer system of
The present invention will now be described in detail with reference to the figures.
The server 112 includes a message transfer agent (“MTA”) 129, i.e. a program function which forwards e-mail, determined not to be spam, received from the firewall or router 110 to the intended recipient/user. For example, MTA 129 can be that of Postfix (trademark of Postfix Corporation) program. The server 112 also includes a known spam detector 121 such as “Spam Assassin” spam detector program. The spam detector 121 may be part of the MTA 129 or a separate program. The spam detector reviews incoming e-mail to detect when the same e-mail (i.e. the same or substantially the same text) is addressed to multiple different recipients/users. The spam detector may ignore e-mails sent from bona fide correspondents, such as employees of a corporation to which the e-mails are sent, such that these e-mails are not considered to be spam. The “bona fide correspondents” may be recorded on a list accessible to the spam detector. But, the same e-mails sent from another entity to multiple recipients/users are assumed to be spam. The user computer 114 may also include an optional spam detector program 123 which identifies spam based on host-based screening software or preferences of the user. The source IP addresses identified by this optional spam detector program 123 result in additional filter rules (each blocking e-mail from a single IP address or range of IP addresses) that can be applied at the firewall or router 110.
FIGS. 2(A) and 2(B) form a flow chart illustrating operation of the spam filter program 119, spam detector 121, optional spam detector 123, range finder program 130 and monitor program 132 in accordance with the present invention. In step 180, an incoming e-mail 125 is received by the firewall or router 110. In response, the spam filter program 119 determines if the source IP address of the e-mail matches any of the active filter rules 117 (decision 182). (Any existing filter rules 117 may have been created in previous iterations of the steps of FIGS. 2(A) and 2(B).) An “active” filter rule is one that has been created and started, but not yet lapsed. As explained below, when a filter rule is created, it is assigned a start time (which is usually immediate upon creation) and a duration/period during which the filter rule is active, i.e. will be enforced. If there is an active filter rule which matches the source IP address of the current e-mail, then the e-mail is blocked, i.e. it is discarded and not permitted to pass through the firewall or router 110 to the server 112 (step 184). However, if the source IP address of the e-mail does not match any of the active filter rules 117, or if there are no active filter rules at this time, then the spam filter program 119 determines if the source IP address of the e-mail matches a lapsed/suspended filter rule, i.e. a filter rule which has not yet been deleted but whose duration/period of activity has lapsed (decision 186). If so, the spam filter program 119 refreshes the start time of the lapsed filter rule to the current time to make it active once again, and defines a new duration/period that was longer than the previous one, for example, twice as long or “x” minutes longer (step 188). (In step 188, the spam filter program 119 also resets a “time to delete” by advancing it an amount equal to the difference between the original start time and the refreshed start time. The purpose of the “time to delete” is described below.) Also, the spam filter program 119 will block this e-mail corresponding to the lapsed/suspended filter rule, and discard it so that it will not pass through the firewall or router 110 to server 112 (step 189). Referring back to decision 186, no branch, if the current e-mail does not match a lapsed/suspended filter rule (or an active filter rule), then firewall or router 110 passes the e-mail through to the mail server 112 with its MTA 129 and spam detector 121 (step 190). Next, the spam detector 121 within server 112 determines if the e-mail appears to be spam, i.e. the same text as other e-mail sent by the same unknown IP source address (decision 204). The spam detector 121 makes this determination by any of numerous well known methods such as comparing text from the same source IP address. This comparison can be made using a hash function on some or all the lines of text of the different e-mails from the same source IP address. Spam may also be assumed when the subject lines of the e-mails from the same IP address are all the same. If the e-mail does not appear to be spam, then the spam detector 121 notifies MTA 129 which forwards the e-mail to its intended recipient indicated in the header of the e-mail, such as client computer 114 (step 205). (In the example illustrated in
Refer again to decision 204 no branch where the server 112 forwards the e-mail to the user computer 114. (In the example illustrated in
The range finder program 130 may reside in server 112 or in another server coupled to server 112 by a network. The range finder program 130 is also coupled by a network to an existing/known Internet service company called “Internet Assigned Number Authority” company or “IANA” 138 (or a similar Internet service). IANA 138 currently maintains a database of all (that is, the range 60.70.80.0 through 60.70.80.127) addresses and the entity that “owns” or registers each block of IP addresses. IANA 138 obtains its IP address ownership information based on the following process. Each entity that desires to use an IP source address on the Internet must first register it with IANA. After the spam detector 121 or spam detector 123 notifies the range finding program 130 of a suspected spammer's source IP address, the range finder program 130 contacts “IANA” (or a similar Internet service) by e-mail and supplies the source IP address of the suspected spammer. (In the example of
Next, the range finding program 130 passes the ranges of blocked, source IP addresses to monitor program 132. (In the example illustrated in
After defining the filter rule (including its time parameters) in step 220 for each range of blocked IP addresses, the monitor program 132 stores the filter rules in an actions database 134, and notifies the firewall or router 110 that a new filter rule has been added to the data base. In response, the spam filter program 119 copies the new filter rule into its local data base, filter rules 117. (In the example illustrated in
Referring again to step 220, when a new filter rule is created, the monitor program 132 also defines a “time to delete” the filter rule (step 220). The “time to delete” the filter rule specifies when to delete the filter rule if spam ceases from the entire range of IP addresses after the duration/period lapses, i.e. after the filter rule is suspended. Consider an example where the filter rule begins immediately, the duration/period of the filter rule is five minutes and the time to delete is fifteen minutes after start. The filter rule will go into effect immediately and last for five minutes. During those initial five minutes, all e-mails from the range of sources IP addresses specified in the filter rule will be blocked and discarded. Then, the filter rule will be “suspended” for the next ten minutes unless and until new spam is detected from any IP address within the range. If spam is detected during these ten minutes from any IP address within the range, then the filter rule is restarted/reactivated. However, if there is no spam from the entire range of IP addresses specified by the filter rule during these ten minutes, then the filter rule will be deleted altogether at the “time to delete” to “clean-out” the database of filter rules (step 250). Step 250 is performed as follows. Whenever, a “time to delete” occurs, an interrupt or alert is sent to the spam filter program 119. The interrupt or alert specifies the corresponding filter rule. In response to the interrupt or delete, the spam filter program 119 confirms that the corresponding filter rule is still lapsed/suspended and if so, deletes the filter rule altogether. (If the corresponding filter rule is still active at the time to delete, then an error has occurred because the original duration/period of the filter rule should have lapsed, and the time to delete should have been advanced when the filter rule was refreshed. In such a case, an administrator will be notified.)
Based on the foregoing, a system, method and computer program for blocking spam has been disclosed. However, numerous modifications and substitutions can be made without deviating from the scope of the present invention. For example, alternative mechanisms for identifying spam may be used. Therefore, the present invention has been disclosed by way of illustration and not limitation, and reference should be made to the following claims to determine the scope of the present invention.
