Possible Clues:

• Hard worker a bit upset the time after Christmas
• Of Troy or its people
• So-called model horse just originally concealed?
• Hard-working, trustworthy person (but, of a horse, untrustworthy!)
• -- horse, a computer program that appears desirable but actually contains something harmful
• Riding provides its conclusion
• A long old war ended at the beginning of the year
• Hard worker? Janitor has lost heart, unfortunately
• This Horse was a hollow invader
• 1996 Rose Bowl mascot