Negative SEO threats have been seen before; recently one was received by Bill Hartzer. People are forwarding these emails to Google, asking what to do. Google told people to not pay them and disavow them. John Mueller from Google posted on Twitter saying that “I’d disavow those links”.
Google even responded to those emails, that it is unclear how credible this threat really is. Google’s algorithms are designed to prevent such activities and causing any problems to webmasters. If we talk about a few specific links, then disavow tool can be used. Google recommends reporting extortion to law enforcement, though it will not do much good if the emails are sent from the countries where countries law enforcement has no control. But if you are receiving these emails on Google, then Google has told to report at https://support.google.com/mail/contact/abuse.
This negative SEO extortion is not at all a new thing. Many cases have been seen before and not specific emails are going out to various site owners and even webmasters.
If you are very much concerned about this thing, then using disavow tool is the solution. But you do need to keep a check on your recent links in Google Webmaster Tools. After that, you can simply disavow them or any other links that concern you. By doing this, you will make it difficult for these guys to hurt your site.
Actually, the real concern is about the Penguin algorithm and all the manual actions regarding the link penalties. The SEO experts and even the webmasters think that it is very easy to perform negative SEO on a site, but in real it is not.
So, don’t worry, if you are one of the receivers of such emails, then just disavow them.