Document.referrer Is that harmful to my website?

[sunvary]

Someone (maybe my Competitors) open a subdomain  on  tumblr.com.

Just like keywordxxx.tumblr.com , and use following script to redirect to my website.

var s=document.referrer; if(s.indexOf("google")>0 || s.indexOf("bing")>0 || s.indexOf("yahoo")>0 || s.indexOf ("aol")>0){ self.location='mywebsiteurl'; }

so , If anyone seach in google ,and click on keywordxxx.tumblr.com , this script will direct the user to my website.   I have found many cases like that, is that harmful ? how can i avoid that?

[MichaelC-15022]

Well, most certainly Google would consider that to be cloaking on the tumblr subdomain.  I'm not sure that the algorithm would spot this and find it to be a problem, but if I were a Google spam engineer, and asked to look at this, it would be very hard to convince me that it wasn't set up deliberately to build traffic to your site.  I would disavow that tumblr subdomain (the subdomain only, e.g. keywordxxx.tumblr.com, DO NOT disavow tumblr.com!).