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PHP Add Captcha Protection To Web Forms

I own a small business website. However, bots started to abusing my forms such as contact.php. How do I stop bad bots from abusing my site? How do I tell if PHP form is submitted by a person or a script?
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Tunneling X Connection Through Intermediate Linux / BSD Gateway

I've ssh gateway behind my NAT firewall. So all users must first login to my gateway host from the internet and then login to other machines on the LAN. This works great for cli based apps. However, few users would like to run x apps from internal LAN hosts and tunnel X display through intermediate ssh gateway and display back output on their local system. For example, from localsystem user makes connection as follows:

ssh -X user@gateway.example.com
ssh -X user@somelan.example.com

X forwarding fails with an error:

Error: Can't open display:

How do I fix this problem and allow users to use X apps with my intermediate Linux / BSD gateway?
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Samba Restrict IPC$ ( list of shared resources )

The IPC$ share allows users to anonymously fetch a list of shared resources from a server. It can be used as a point of attack into a system. How do I disable or limit IPC$ under Samba to certain subnet such as
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What Is The Difference Between Authentication And Authorization?

What is the difference between authentication and authorization? Why it is important to understand difference between the two? Authentication vs. Authorization -- what are they and how do they differ?
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Find the DNS Authority Record for a DNS Domain (SOA)

Q.How do I find out the DNS authority record (SOA) for any DNS domain under UNIX / Linux shell?
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How to: MySQL Delete Column

How do I delete a column from an existing MySQL table using UNIX / Windows / Linux mysql command line utility sql syntax?
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Can I Use Multiple Virtualization Technologies Simultaneously under Linux?

Q. I was reading this article and wanted to try out KVM, XEN, VMWare and VirtualBox simultaneously on my desktop system with 2GB RAM? Why I'm not able to use run multiple virtualization technologies simultaneously under Ubuntu Linux? Can a powerful Linux server run multiple virtualization technologies simultaneously?
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Linux / UNIX: Ping a Block of Hosts (netblock)

Q. How do I ping a block of hosts such as
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Domain Redirection Using a PHP Script

Q. How do I redirect my domain name using a php server side scripting under Apache web server?
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Windows Delete File Securely / Permanently Delete File Data

Q. I know how to delete a file securely using GNU/Linux and Open source tools under Linux. I'm looking for DoD 5520.22-M or NNSA NAP-14.x.secure compliant delete utility under Windows. How do I delete a file permanently under Windows XP or Server operating system with NTFS; so that no one can retrieve my data?
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