I read that using the post method is not so much secure, and others can crack your site, and SSL or TSL was suggested to get when you want to create a dynamic web site. Can anyone give some more info about this topic?
SSL, or secure sockets layer, is really only necessary when passing sensitive info over a form (such as credit card #, SSN, etc.). You don't need it for just a dynamic website, or even for a contact form. But if you want one, you can buy one here: http://www.digicert.com/ But there are lots of companies that sell them now, just google for one.
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You should not use SSL/TLS with dynamic website unless it is exchanging some secret information such as credit card numbers, etc as SSL/TLS causes extra CPU loads on clients and server and can slow up your website in some extent. However, if you use SSL/TLS then no one can make eavesdropping with your website.
SSL simply allows encrypted communications between client (the browser) and your server. As others have said, most useful when entering personal information, logins, or payment information. It helps stop sniffing of that data off the network (particularly with wireless networks, and public wifi too). There's a few different types of certificate available, depending on your need - if it's just for a private login area, or you're doing transactions for hundreds/thousands of dollars. The certs can be bought for anything from $10 to $1000 and up.