JS_Obfus.TRSA is a malicious JavaScript file that may be downloaded from remote site(s). It may be hosted on a Web site and run when a user accesses the said Web site.

It uses RSA algorithm for encryption. Once an unsuspecting user visits an affected Web page, it connects to a Web site to download a file detected by Trend Micro as TROJ_INJECT.XAXT.

Technical details can be found at this Trend Micro page.