Trojan horse on my tumblr blog

I never had a problem with my blog,but when i tried to log in yesterday
avast wouldn’t allow me to log in because of a trojan horse it detected
how did that hapenned and how can i fix it?
is it a false alarm or something?
my blog is on http://www.tumblr.com/
these are the details: Processfile://C:\Program Files\Google\Chrome\Ap…
Infection:js:Decode-XB [Trj]

hey according zulu is a risky url

http://zulu.zscaler.com/submission/show/c9bc79b434854c84004e7ac72021c525-1366217694

according to Zulu it is benign…