Should I disavow links to a dead sub domain?

[rubennunez]

I'm analyzing a client's website today and I found that they have over 300 spammy sites linking to a subdomain of their main site. So for example, say their site is clientsite.com, well they have hundreds of links pointing to deadsite.clientsite.com.

That subdomain was used at one time as a staging site, and is no longer active.

Are those hundreds of spammy sites hurting or potentially hurting my client's SEO? Or is it a non-issue because the links point to a dead subdomain?

We believe that that staging sub domain site was hacked at one time, and thats where all those spammy links came from.

Should I disavow them?

[JordanLowry]

I would recommend disavowing all the spammy links just to be on the safe side. However subdomains can be treated as a seperate site all together and if there is no instance of internal links being placed on the subdomain pointing to the main domain you may be fine. However I like to be safe so I would probably disavow the backlinks.

[rubennunez]

Thanks. There are no links being shared between the main domain and the subdomain, and none of those links actually point to the main domain.

Would disavow even be of any use though? I though that a disavow file had to be for the specific domain, so adding a disavow to all those links wouldn't do anything.

[mediawyse]

You said this:

"Would disavow even be of any use though? I though that a disavow file had to be for the specific domain, so adding a disavow to all those links wouldn't do anything"

When you disavow at the domain level, you also cover ALL the subdomains on that domain as well (even if they are deleted). So the best practice in this case, even if the domain isn't there anymore would be to just disavow those links.

John Mueller clarified this in a Google+ thread back in 2014.