Gathering of addresses

In order to send spam, spammers need to obtain the e-mail addresses of the intended recipients. To this end, both spammers themselves and list merchants gather huge lists of potential e-mail 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 inaccurate. A single spam run may target tens of millions of possible addresses — many of which are invalid, malformed, or undeliverable.

Sometimes, if the sent spam is "bounced" or sent back to the sender by various programs that eliminate spam, or if the recipient clicks on an unsubscribe link, that may cause that email address to be marked as "valid", which is interpreted by the spammer as "send me more".

Blacklisting

Attempts to stop spam by blacklisting sender's IP addresses still allows a small percentage through. Most IP addresses are dynamic, i.e. they are frequently changing. An ISP, or any organization directly connected to the Internet, gets a block of real Internet addresses when they register in the DNS. Within that block, they assign individual addresses to customers as needed. A dial-up customer may get a new IP address each time they connect. By the time that address appears on blacklists all over the world, the spammer will have new addresses for the next run. There are 4 billion possible IPv4 addresses on the Internet. The game of keeping up with these rapidly changing IP addresses has been facetiously called "whack-a-mole".

So called policy lists are black lists that contain IP addresses on a preventive basis. An IP address can be listed therein even if no spam has ever been sent from it, because it has been variously classified as a dial-up address, end-user address, or residential address, with no formal definition of such classification schemes. Not requiring evidence of spam for each enlisted address, these lists can collect a greater number of addresses and thus block more spam. However, the policies devised are not authoritative, since they have not been issued by the legitimate user of an IP address, and the resulting lists are therefore not universally accepted.

Microsoft Reciprocal License (Ms-RL)

This Microsoft license allows for distribution of derived code so long as the modified source files are included and retain the Ms-RL. The Ms-RL allows those files in the distribution that do not contain code originally licensed under Ms-RL to be licensed according to the copyright holder's choosing. This is equivalent to the CDDL or LGPL (GPL with a typical "linking exception"). Initially known as the Microsoft Community License, it was renamed during the OSI approval process.

On December 9, 2005, the Ms-RL license was submitted to the Open Source Initiative for approval by John Cowan. OSI then contacted Microsoft and asked if they wanted OSI to proceed. Microsoft replied that they did not wish to be reactive and that they needed time to review such a decision.

At the O'Reilly Open Source Convention in July 2007, Bill Hilf, director of Microsoft's work with open source projects, announced that Microsoft had formally submitted Ms-PL and Ms-RL to OSI for approval. It was approved on October 12, 2007 along with the Ms-PL. According to the Free Software Foundation, it is a free software license. However, unlike the Microsoft Public License, it is not compatible with the GNU GPL.

Concurrent Versions System

In the field of software development, the Concurrent Versions System (CVS), also known as the Concurrent Versioning System, provides a version control system based on open-source code. Version control system software keeps track of all work and all changes in a set of files, and allows several developers (potentially widely separated in space and/or time) to collaborate. Dick Grune developed CVS in the 1980s. CVS has become popular in the open source software world and is released under the GNU General Public License.