Troj/Zapchas-J is an mIRC-based backdoor Trojan. The Trojan creates several files in the Windows\system folder. One of these files, svchost.exe, is a renamed copy of the mIRC application, one is a mIRC script file (also detected as Troj/Zapchas-J) and the remainder are configuration settings for the Trojan.

More information can be found at this Sophos page.