White HAT SEO

White HAT SEO  i.e SEO practices which completely follow the guidelines of various major search engines. It has a very low risk in getting red flags from the search engines.

Black HAT SEO:

In this method we practice techniques which completely violate the guidelines of majority of the search engines. The risk of getting banned is high.

Grey HAT SEO

As far as SEO is concerned, there is a very thin line between White HAT SEO and Black HAT SEO and that portion belongs to the Grey HAT SEO methods and Techniques. Some of the Grey Hat SEO techniques are mentioned here

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Gray Hat SEO is difficult to define. According to my point of view, Grey Hat SEO is a combination of Black Hat and White Hat SEO. SEO consultant is defined in different ways, according to SEO Consultant John Andrews Gray Hat SEO is not something between Black Hat and White Hat, but rather "the practice of tactics/techniques which remain ill-defined by published material coming out of Google and for which reasonable people could disagree on how the tactics support or contrast with the spirit of Googles published guidelines."

We can not say that Black Hat SEO is going to violate Google's guidelines or not, it's probably best to avoid that tactic. Every marketer needs to evaluate risk versus reward on their own terms, but with Google's algorithms getting stricter and stricter all the time, your safest route as a business is going to be strictly white hat SEO. If you want to know more about Black Hat SEO go here- http://positionly.com/blog/seo/grey-hat-seo-techniques

Grey Hat SEO

The term "grey hat" refers to a computer hacker or computer security expert who may sometimes violate laws or typical ethical standards.

Gray hat SEO is the techniques that take more risks & do not face the wrath of search engines and get banned. Grey hat SEOs generally try to see what they can get away with & also remember that search engines keep on changing their policies and what is classified as a grey hat SEO technique today may be considered as a black hat SEO technique tomorrow.

The tactics used by grey hat SEOs is to exploit the vulnerabilities in the ranking algorithms followed by search engines like Google and Bing.

Examples of grey hat SEO techniques are: Google bombing/washing, spinning/rewriting of articles, reciprocal links, buying old or expired domains, use of cloaking web pages etc.

Grey Hat SEO Technique:

Spam Comments: Spam comments are intended to create free backlinks. These Links are 100% nofollow and transfer no SEO juice, which makes this technique a real waste of time. Spam comments also harm your blog by making it look neglected and unprofessional.

Duplicate Content: Duplicate content means copy and paste content creation practice across domains. It means the blocks of copied content from different sources exactly match each other or look very much alike. Duplicate content concerns not only different domains but also one domain.

Cloaking : A search engine technique that presents completely different content or URL to the user than to the search engine spider. This SEO method is considered deceptive because it tricks search engines in order to get the desired ranks for target keywords.

Grey Hat SEO-A practice or technique used to increase the website's ranking with some illegal/ wrong methods which are not defined by Google or we can say that it lies between White Hat and Black Hat SEO.

And Yes, they are riskier for the websites.It is suggested that not to practice Grey Hat SEO, as it creates a bad effect on your Search Engine Rankings.

Some examplea of Grey Hat SEO are-Doorway Pages, Cloaking, Duplicate content etc.