Step 1: Understand the question.
We need the malware that spreads without attaching itself to a host file.
Step 2: How a virus spreads.
A virus must attach to a host file or program. It becomes active only when that file is opened or run, so it needs a host.
Step 3: How a worm spreads.
A worm is a standalone program. It copies itself and travels through networks on its own, with no host file needed.
Step 4: How a Trojan works.
A Trojan hides inside a program that looks useful and tricks the user into running it. It does not self spread like a worm.
Step 5: How spyware works.
Spyware secretly watches the user and steals information, but it does not spread by itself across networks.
Step 6: Conclude.
The one that spreads on its own without a host file is the worm, which is option 2.
\[ \boxed{\text{Worm}} \]