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Email bomb

Mass mailing

Mass mailing consists of sending numerous duplicate mails to the same email address. These types of mail bombs are simple to design but their extreme simplicity means they can be easily detected by spam filters. Email-bombing using mass mailing is also commonly performed as a DDoS attack by employing the use of "zombie" botnets; hierarchical networks of computers compromised by malware and under the attacker's control. Similar to their use in spamming, the attacker instructs the botnet to send out millions or even billions of emails, but unlike normal botnet spamming, the emails are all addressed to only one or a few addresses the attacker wishes to flood. This form of email bombing is similar in purpose to otherDDoS flooding attacks. As the targets are frequently the dedicated hosts handling website and email accounts of a business, this type of attack can be just as devastating to both services of the host.

This type of attack is more difficult to defend against than a simple mass-mailing bomb because of the multiple source addresses and the possibility of each zombie computer sending a different message or employing stealth techniques to defeat spam filters.

[edit]List linking

List linking means signing a particular email address up to several email list subscriptions. The victim then has to unsubscribe from these unwanted services manually. In order to prevent this type of bombing, most email subscription services send a confirmation email to a person's inbox when that email is used to register for a subscription. This method of prevention is easily circumvented: if the perpetrator registers a new email account and sets it to automatically forward all mail to the victim, he or she can reply to the confirmation emails, and the list linking can proceed.

[edit]Zip bombing

A ZIP bomb is a variant of mail-bombing. After most commercial mail servers began checking mail with anti-virus software and filtering certain malicious file types, EXE, RAR, Zip, 7-Zip, mail server software was then configured to unpack archives and check their contents as well. A new idea to combat this solution was composing a "bomb" consisting of an enormous text file, containing, for example, only the letter z repeating millions of times. Such a file compresses into a relatively small archive, but its unpacking (especially by early versions of mail servers) would use a greater amount of processing, which could result in a DoS (Denial of Service).

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How Does Facebook Work?

Social networking is the art of connecting with those who share common interests. Your “˜network’ is a community that helps keep you united with others and offers many benefits. Networking via social media sites has revolutionized how we use the Internet and is at the forefront of what we now call Web 2.0.

Facebook is social networking. People have been “facebooking” each other for about 6 years now, making Facebook the most used social network with over 350 million users worldwide. But how does Facebook work?

In this article, I will discuss Facebook’s inner workings, covering its architecture and frontend/backend infrastructure””the nuts and bolts that hold Facebook together.

How Does Facebook Work?””The Front End

Facebook uses a variety of services, tools, and programming languages to make up its core infrastructure. At the front end, their servers run a LAMP (Linux, Apache, MySQL, and PHP) stack with Memcache. Not a computer science expert? Let’s take a look at exactly what that means.

Linux & Apache

This part is pretty self-explanatory. Linux is a Unix-like computer operating system kernel. It’s open source, very customizable, and good for security. Facebook runs the Linux operating system on Apache HTTP Servers. Apache is also free and is the most popular open source web server in use.

MySQL

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For the database, Facebook utilizes MySQL because of its speed and reliability. MySQL is used primarily as a key-value store as data is randomly distributed amongst a large set of logical instances. These logical instances are spread out across physical nodes and load balancing is done at the physical node level.

As far as customizations are concerned, Facebook has developed a custom partitioning scheme in which a global ID is assigned to all data. They also have a custom archiving scheme that is based on how frequent and recent data is on a per-user basis. Most data is distributed randomly.

PHP

Facebook uses PHP because it is a good web programming language with extensive support and an active developer community and it is good for rapid iteration. PHP is a dynamically typed/interpreted scripting language.

Memcache

Memcache is a memory caching system that is used to speed up dynamic database-driven websites (like Facebook) by caching data and objects in RAM to reduce reading time. Memcache is Facebook’s primary form of caching and helps alleviate the database load.

Having a caching system allows Facebook to be as fast as it is at recalling your data. If it doesn’t have to go to the database it will just fetch your data from the cache based on your user ID.

Downsides to Using LAMP

Facebook has realized that there are downsides to using the LAMP stack. Notably, PHP is not necessarily optimized for large websites and therefore hard to scale. Also, it is not the fastest executing language and the extension framework is difficult to use.

Mike Schroepfer, Facebook’s Vice President of Engineering, recently did an interview atEmTech@MIT concerning this. “Scaling any website is a challenge,” Schroepfer said, “but scaling a social network has unique challenges.”

He went on to say that unlike other websites, you can’t just add more servers to solve the problem because of Facebook’s “huge interconnected dataset.” New connections are created all the time due to user activity.

Facebook has grown so quickly that they are often faced with issues regarding database queries, caching, and storage of data. Their database is huge and largely complex. To account for this, Facebook has started a lot of open source projects and backend services.

How Does Facebook Work?””The Back End

Facebook’s backend services are written in a variety of different programming languages including C++, Java, Python, and Erlang. Their philosophy for the creation of services is as follows:

1. Create a service if needed

2. Create a framework/toolset for easier creation of services

3. Use the right programming language for the task

A list of all of Facebook’s open source developments can be found here. I will discuss a few of the essential tools that Facebook has developed.

Thrift (protocol)

Thrift is a lightweight remote procedure call framework for scalable cross-language services development. Thrift supports C++, PHP, Python, Perl, Java, Ruby, Erlang, and others. It’s quick, saves development time, and provides a division of labor of work on high-performance servers and applications.

Scribe (log server)

Scribe is a server for aggregating log data streamed in real-time from many other servers. It is a scalable framework useful for logging a wide array of data. It is built on top of Thrift.

Cassandra (database)

Cassandra is a database management system designed to handle large amounts of data spread out across many servers. It powers Facebook’s Inbox Search feature and provides a structured key-value store with eventual consistency.

HipHop for PHP

HipHop for PHP is a source code transformer for PHP script code and was created to save server resources. HipHop transforms PHP source code into optimized C++. After doing this, it uses g++ to compile it to machine code.

Conclusion

In a nutshell, that’s Facebook. This article could easily be 37 pages longer if I were to go into more detail, but to answer the question “How does Facebook work?” I think this will suffice. If you look past all of the features and innovations the main idea behind Facebook is really very basic””keeping people connected. Facebook realizes the power of social networking and is constantly innovating to keep their service the best in the business.

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NComputing

NComputing is a desktop virtualization company that manufactures hardware and software to create virtual desktops (sometimes called zero clients or thin clients) which enable multiple users to simultaneously share a single operating system instance.

NComputing, based in Redwood City, CA is a privately held for-profit company with offices in the United States, Australia, Canada, China,Germany, India, Korea, Poland, Russia, Spain and the United Kingdom; and resellers around the world

Founding the company

In 2003, Young Song, a former VP at eMachines, met German entrepreneur Klaus Maier (formerly CEO of hydrapark), who had spent more than ten years developing the core software on which NComputing is based.^[2] They formed a team to develop the complementary hardware in Korea, while the software was written in Poland and Russia. After they successfully launched the product and reached $10M revenue in two years, the two founders decided to move its headquarters to Silicon Valley. Stephen Dukker, former chairman of eMachines, joined NComputing in August 2006, to lead the company.^[3]

[edit]Financing

Dukker introduced NComputing to venture capitalists and technology journalists in September 2006 at DEMOfall 06.^[4] By October 2006, NComputing had raised $8 million from Scale Venture Partners (formerly known as BA Venture Partners).^[5] In January 2008, the company raised a $28 million series B round of financing,^[6] led by Silicon Valley venture capital firmMenlo Ventures with participation from Scale Venture Partners and South Korea’s Daehong Technew Corp.

[edit]Current growth

The company was founded in 2004 and is the fastest growing desktop virtualization company in the world with over 20 million daily users in 140 countries. It has deals with 40,000 education and business organizations in 140 countries^[7] including 5,000 school districts in the United States. NComputing has shipped more than three million units overall,^[8] including 180,000 seats to provide one computing seat for every K–12 student in the country of Macedonia.^[9] NComputing sells its solutions through value-added resellers around the world.^[10] As of 2010, the company has 200 employees worldwide.^[11]

[edit]Products

The combination of NComputing hardware (access devices, thin clients, zero clients) and virtualization software (vSpace desktop virtualization software) use the excess computing capacity of one PC or server to create multiple virtual desktops.^[7]

The vSpace software allows multiple simultaneous user accounts to run on a single operating system instance. The access devices connect each user’s keyboard, monitor, and mouse to the shared host. Each NComputing access device has ports for a keyboard, monitor, and mouse, but does not contain a CPU nor memory.^[7] vSpace can either be deployed alone or in concert with other virtual desktop infrastructure software solutions (including Citrix, VMware and Microsoft).

The company offers three product lines, the X-series, L-series, and U-series, as well as an OEM chip.

[edit]X-series - Direct Connect

X-series access devices connect via CAT 5 cable to a PCI card that is installed in a shared PC. The technology supports up to two PCI cards. The maximum distance between the PC and an access device is 10 m (33 ft). The X-series comes in kits which include one PC card and several access terminals, depending on the specific product.^[12]

In a test published by Computer Aid International in April 2009 and conducted by three African universities, the X300 turned out to be the preferred solution when setting up computer labs.^[13]

[edit]L-series - Ethernet connect

Unlike the X-series, the NComputing L-series does not use a PCI card. L-series access devices connect each user’s keyboard, mouse,USB foot Padle and monitor back to the shared PC over standard Ethernet cables through a router or switch. An entry-level server supports approximately 30 users.^[14] The L-series comes in kits that include NComputing’s vSpace software and one access device.

[edit]U-series - USB connections

The U-series are the simplest of all to connect, because they connect into USB ports on the host computer, and thus no network switches or PCI cards are required. USB has an inherent distance limt.

[edit]vSpace Server software

NComputing’s vSpace Server virtualization software, included with the hardware, creates the virtual desktops in the shared PC by dividing the computer's resources into independent sessions that give each user their own PC experience.^[7] The vSpace software uses the company’s proprietary display and communications protocol ("UXP") to communicate between the shared computer and the user stations. UXP serves a similar purpose as Microsoft’s RDP and Citrix’s ICA.

[edit]Operating system support

[edit]Linux support

Linux is supported through a version of vSpace Server for Linux software. Currently, NComputing offers support for Ubuntu 10.04.3 32-bit and 64-bit for the L300 and Ubuntu 10.04.2 32-bit for the X350. The vSpace Server software and hardware clients require registration after 30 days for product upgrade notification. ^[15]

[edit]Windows support

Windows is supported through a version of vSpace Server for Windows software.  The supported versions of Windows include: Windows Server 2003 R2 SP2, Windows XP SP3 (32-bit); Windows Server 2008 SP2, Windows Vista SP21(32-bit); Windows Server 2008 R2 SP1, Windows MultiPoint Server 2011, Windows 7 SP1 (both 32- and 64-bit). The vSpace Server software and hardware clients require registration after 30 days for product upgrade notification.

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