Realistically, it is about as safe to use a credit card over the Internet as it would be to use one over the telephone. Data moves across the Internet in clear text. Encryption makes reading intercepted data extremely difficult. SSL is designed to allow encrypted, authenticated communication across the Internet. Be sure the site you do business with not only has security but also actually uses it.
Many networks prohibit sending such mail traffic in an acceptable use or security policy.
This is much more difficult than it sounds. Back to Topics I think one of my students copied their term paper off the Internet. According to Wallace Wang in a Boardwatch magazine article, over the last couple of years a number of web sites began selling pre-written term papers, theses and research works. A few companies will actually write a paper from scratch for a customer. These papers are not kept online.