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Protection From Spammers

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Spam is sending identical or nearly identical messages to thousands (or millions) of recipients. Addresses of recipients are often harvested from Usenet postings or web pages, obtained from databases, or simply guessed by using common names and domains. By definition, spam is sent without the permission of the recipients.

Overview

Sending spam violates the Acceptable Use Policy (AUP) of almost all Internet Service Providers, and can lead to the termination of the sender's account. Many jurisdictions, such as the United States of America, which regulates via the CAN-SPAM Act of 2003, regard spamming as a crime or as an actionable tort.

As the recipient directly bears the cost of delivery, storage, and processing, one could regard spam as the electronic equivalent of "postage-due" junk mail. However, the Direct Marketing Association will point to the existence of "legitimate" e-mail marketing. Most commentators classify e-mail-based marketing campaigns where the recipient has "opted in" to receive the marketer's message as "legitimate".

Spammers frequently engage in deliberate fraud to send out their messages. Spammers often use false names, addresses, phone numbers, and other contact information to set up "disposable" accounts at various Internet service providers. They also often use falsified or stolen credit card numbers to pay for these accounts. This allows them to move quickly from one account to the next as the host ISPs discover and shut down each one.

Spoofing

Spammers frequently go to great lengths to conceal the origin of their messages. They do this by spoofing e-mail addresses (much easier than Internet protocol spoofing). The spammer hacks the email protocol (SMTP) so that a message appears to originate from another email address. Some ISPs and domains require the use of SMTP-AUTH, allowing positive identification of the specific account from which an e-mail originates.

Spammers cannot completely spoof an e-mail address chain, since the receiving mailserver records the actual connection from the last mailserver's IP address; however, spammers can forge the rest of the ostensible history of the mailservers the e-mail has ostensibly traversed. But tracing an email message's route is usually fruitless since many ISPs have thousands of customers and identifying just one spammer is tedious.

Spammers frequently seek out and make use of vulnerable third-party systems such as open mail relays and open proxy servers. The SMTP system, used to send email across the Internet, forwards mail from one server to another; mail servers that ISPs run commonly require some form of authentication that the user is a customer of that ISP. Open relays, however, do not properly check who is using the mail server and pass all mail to the destination address, making it quite a bit harder to track down spammers.

Increasingly, spammers use networks of virus-infected Windows PCs (zombies) to send their spam. Zombie networks are also known as Botnets.

Spoofing can have serious consequences for legitimate email users. Not only can their email inboxes get clogged up with "undeliverable" emails in addition to volumes of spam, they can mistakenly be identified as a spammer. Not only may they receive irate email from spam victims, but (if spam victims report the email address owner to the ISP, for example) their ISP may terminate their service for spamming.

Gathering of addresses

In order to send spam, spammers need to obtain the email addresses of the intended recipients. Toward this end, both spammers themselves and list merchants gather huge lists of potential email addresses. Since spam is, by definition, unsolicited, this address harvesting is done without the consent (and sometimes against the expressed will) of the address owners. As a consequence, spammers' address lists are remarkably inaccurate. A single spam run may target tens of millions of possible addresses -- many of which are invalid, malformed, or undeliverable.

Avoiding spam

Computer users can avoid e-mail spam in several ways.

Perhaps the best way to avoid spam involves avoiding making one's email address available to spammers, directly or indirectly. Basic computer literacy should include an understanding of the basics of spamming and spam-avoidance. One should never reply to a spam email, or click an "opt-out" link (this simply confirms that an email address is "live"). Users should not reveal their e-mail addresses on porn, warez and other shady sites.

If a web site requests registration in order to allow useful operations, such as posting in Internet forums, a user may give a temporary disposable address - set up and used only for such a purpose - periodically deleting such temporary email accounts from their e-mail servers. (Users should notify such forums of the new replacement addresses if they wish to continue interaction for valid purposes.)

Anti-spam programmers have released several tools - intended for both end users and for systems administrators - which automate the highlighting, removal or filtering of e-mail spam by scanning through incoming and outgoing e-mails in search of traits typical of spam

Challenge/response spam filtering

Description: This "selfish" method of spam filtering replies to all email with a "challenge" - a message only a living person can (theoretically) respond to. There are several problems with this method which have been well known for many years.

Glitch Busters abandoned this method of filtering after a short test period.

This is almost funny. While it doesn't affect all C-R systems, there are those that are vulnerable.

How do two C-R system users ever start talking to each other?

User A sends mail to user B. While user B's address is then known to A, user B's C-R server's mail is not.
User B's C-R system sends a challenge to A...
...who intercepts the challenge with A's C-R system, which sends a challenge to user B's C-R system...
Rinse, wash, repeat....

Bayes algorithm filtering

POPFile is an automatic mail classification tool. Once properly set up and trained, it will scan all email as it arrives and classify it based on your training. You can give it a simple job, like separating out junk e-mail, or a complicated one like filing mail into a dozen folders. Think of it as a personal assistant for your inbox.

POPFile classifies email into categories you define. It can sort into spam and not spam or into any number of categories you like (e.g. work, personal, important project, hobby, etc.).

The classification is done using a naive Bayes algorithm. In other words, POPFile uses statistics to track which words are likely to appear in which messages. This means that POPFile will adapt to the kind of mail you receive and needs to be trained. Out of the box, it doesn't know anything about spam or how messages from your mother differ from those your friends send you. However, if you train it, it will soon learn how to tell these different kinds of messages apart.
Get POPFile

Disposable E-mail Accounts