Troj_Chepvil.RAR Trojan is a compressed RAR attachment received through a certain spam email.

The said email provides a password that is used to extract the attachment's .EXE content, which Trend Micro detects as TROJ_CHEPVIL.C. The attachment is compressed in RAR format.

As a result, once a user extracts and executes the contents of the compressed attachment, routines of the extracted Trojan are also exhibited on the affected system.

Technical details can be found at this Trend Micro page.