A common synonym for spam is
e-mail (UBE). Definitions of spam
usually include the aspects that email is
unsolicited and sent in bulk. "UCE" refers
specifically to "unsolicited commercial
E-mail spam slowly but
exponentially grew for several decades to
several billion messages a day.
frustrated, confused, and annoyed e-mail
users. Laws against spam have been
sporadically implemented, with some being
opt-out and others requiring opt in
The total volume of spam (over 100 billion
emails per day as of April 2008) has leveled
off slightly in recent years, and is no
longer growing exponentially. The amount
received by most e-mail users has decreased,
mostly because of better filtering.
About 80% of all spam is sent
by fewer than 200 spammers. Botnets,
virus-infected computers, are used to send
about 80% of spam. The cost of spam is borne
mostly by the recipient, so it is a form of
postage due advertising.
E-mail addresses are collected from
chatrooms, websites, newsgroups, and
which harvest users' address books, and are
sold to other spammers. Much of spam is sent
to invalid e-mail addresses. ISPs have
attempted to recover the cost of spam
through lawsuits against
they have been mostly unsuccessful in
collecting damages despite winning in court.
Spam has several definitions, varying by the
Unsolicited bulk e-mail (UBE)—unsolicited
e-mail, sent in large quantities.
Unsolicited commercial e-mail (UCE)—this
more restrictive definition is used by
regulators whose mandate is to regulate
commerce, such as the U.S. Federal Trade
Any email message that is fraudulent.
Any email message where the sender’s
identity is forged, or messages sent though
unprotected SMTP servers, unauthorized
proxies, or botnets (see Theft of service
spam e-mails contain URLs to a website
or websites. According to a Commtouch report
in June 2004, "only five countries are
hosting 99.68% of the global spammer
websites", of which the foremost is China,
hosting 73.58% of all web sites referred to
Most common products advertised
According to information compiled by
E-mail spam for 2006
can be broken down as follows.
Main article: Anti-spam techniques (e-mail)
The U.S. Department of Energy Computer Incident Advisory
Capability (CIAC) has provided specific countermeasures against
electronic mail spamming.
Some popular methods for
filtering and refusing spam include
e-mail filtering based on the content of the e-mail, DNS-based
blackhole lists (DNSBL), greylisting, spamtraps, Enforcing
technical requirements of e-mail (SMTP), checksumming systems to
detect bulk email, and by putting some sort of cost on the
sender via a Proof-of-work system or a micropayment. Each method
has strengths and weaknesses and each is controversial due to
One method employed involves using a white list of
addresses. For example, the owner of the email account can set
the server to only allow emails from senders that are in the
owner's addressbook. This is often used in combination with
methods to give new senders an opportunity to request inclusion
in the owner's addressbook.
1. All email originating from senders not in the addressbook are
sent an automatic response stating that their email has not
reached the recipient (ie. the email account owner).
2. The sender is given the option of sending the recipient an
addressbook inclusion request via an online form.
3. The online form includes a captcha to only allow requests
from human (non-computer-automated) sources.
4. If the recipient (account owner) approves the request,
current and future email from the sender reaches the recipient
with no further filtering.
Yahoo dropped a similar feature from their webmail service in
Anti-spam techniques should not be employed on abuse@
addresses, as is commonly the case. The result of this is that
when people attempt to report spam to a host, the spam message
is caught in the spam filter and the host remains unaware that
their network is being exploited by spammers.
In 2003, spam investigators saw a radical change in the way
spammers sent spam. Rather than searching the global network for
exploitable services such as open relays and proxies, spammers
began creating "services" of their own. By commissioning
computer viruses designed to deploy proxies and other
spam-sending tools, spammers could harness hundreds of thousands
of end-user computers. The widespread change from Windows 9x to
Windows XP for many home computers, which started in early 2002
and was well under way by 2003, greatly accelerated the use of
home computers to act as remotely-controlled spam proxies. The
original version of Windows XP as well as XP-SP1 had several
major vulnerabilities that allowed the machines to be
compromised over a network connection without requiring actions
on the part of the user or owner. While Windows 2000 had
similar vulnerabilities, that operating system was never widely
used on home computers.
Most of the major Windows e-mail viruses of 2003, including the
Sobig and Mimail virus families, functioned as spammer viruses:
viruses designed expressly to make infected computers available
as spamming tools.
Besides sending spam, spammer viruses serve spammers in other
ways. Beginning in July 2003, spammers started using some of
these same viruses to perpetrate distributed denial-of-service
(DDoS) attacks upon DNSBLs and other anti-spam resources.
Although this was by no means the first time that illegal
attacks have been used against anti-spam sites, it was perhaps
the first wave of effective attacks.
In August of that year, engineering company Osirusoft ceased
providing DNSBL mirrors of the SPEWS and other blocklists, after
several days of unceasing attack from virus-infected hosts.
The very next month, DNSBL operator Monkeys.com succumbed to the
attacks as well. Other DNSBL operators, such as Spamhaus,
have deployed global mirroring and other anti-DDoS methods to
resist these attacks.
Zombie networks are particularly active in North America where
about half of the Internet users are on a broadband connection
and many leave their computers on all the time. In January,
2008, 8% of all e-mail spam was sent by the Storm botnet,
created by the Storm Worm, first released in January, 2007.
It is estimated that as many as 1 million or more computers have
been infected and their owners are unwilling and unknowing
participants. In the 3rd quarter of 2008 almost one in every 400
email messages contained a dangerous attachment, designed to
infect the recipient’s computer, eight times as often as in the
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