Troj/ExpJS-N is a malicious JavaScript embedded in a web page.
When a page containing Troj/ExpJS-N is viewed in a browser, the malicious script attempts to exploit client vulnerabilities in order to infect the user with further malware.
Troj/ExpJS-N has been seen associated with the Operation Aurora exploit of the zero-day Microsoft Internet Explorer vulnerability (CVE-2010-0249 patched by MS10-002).