Existing Information Sources: Threat Trends Sample Clauses

Existing Information Sources: Threat Trends. 2.1.1 SPAM Spam is unsolicited and bulk email sent without the verified permission of the receiver. Delivery failure messages, misdirected messages and messages from system administrators are examples of unsolicited emails which are not spam. Spammers use lists of email addresses that have been harvested using different methods, for example, crawling web pages, using search engines, sending chain emails, attacking dictionaries by sending blank spam, analysing domain queries and using malwares or bots. Different spam techniques and the content of spam have evolved over time as spam filters have become able to detect spam. Usually this is done through analysing spam content such as the subject or body part of the email. First examples of spam included plain text messages and identifying identical plain text sent in large quantities was not a big problem. Personalised emails (emails that include the receiver’s name, e.g. "Dear Xxxx" etc.), spam obfuscation (e.g. changing "Viagra" to "v1agra"), American Standard Code for Information Interchange (ASCII) art and HyperText Markup Language (HTML) emails constituted the next steps in the evolution of spam content. Another method to bypass spam filters is using images in the message content. Spammers also use animated images or add noise to image spam. Also, blank spam is sent to identify true email addresses. If a blank mail is sent to a false address it is returned with a system or server or user error. If the blank mail is not returned, the email address is real. Blank spam may also include hidden HTML or JavaScript codes to download malware. As spam content evolves, different countermeasures are taken to reduce spam activities. While there is no single way to stop spam, different approaches exist to reduce the amount of spam that is received. These include rejecting emails from domains/IPs that are likely to send spam (black/white listing, DNS-based Blackhole Lists (DNSBLs), DNS Sender Policy Framework (SPF) records, filtering the outgoing Simple Mail Transfer Protocol (SMTP) port, grey listing etc.), more advanced methods like analysing message content and deciding whether an email is spam. Another measure to counter spam is deploying a honeypot. This is a computer system which imitates an open mail relay or an open proxy server. A spammer who probes the network for an open mail relay or a proxy server will try to send spam through the honeypot and thus reveal some information about their identity. Received spa...