Legitimately getting links for the purpose of SEO is a time consuming task. It involves writing quality content and then taking the time to properly market and promote that content. That often involves contacting other bloggers and social network promotion. That is the white hat way. Unfortunately a lot of people find it easier to employ black hat techniques to get a jump in the rankings. This generally doesn’t end well and should be avoided. Here are a few of them:
Cloaking is where one set of content is presented to search engine spiders and a completely different page is shown to actual visitors. One example is where a user searches for “blue widgets” and the page that loads is an advert for porn.
There are plugins that will allow you to pull content from RSS feeds. While this does give you a lot of free content, there is a high likelihood of being penalized for duplicate content. A lot of these are available as plugins on platforms like WordPress.
Trackback links are automatic links which point to sites that have linked to that page. Too many links from trackback links or to unrelated content could also mean penalties. If you are linking to pages that have trackback links, ensure that the subject matter is related.
These are a set of web 2.0 properties linked to each other and ultimately to a page of your choosing. In a diagram they would resemble a wheel with the center point missing and each of the spokes links to the various properties.