How can I download free movies from the net without catching malware?
Streaming is the only safe, free and legal way to get a hold of movies for free (in general). Studios obviously aren't keen on just giving out movies for free.
the safest way to download movies online is
1. to only download movies that you can download legally, e.g. pay for it or download old movies, or movies with a Creative Commons license.
2. to stream movies rather than downloading them.
3. to use anti-virus and anti-malware software on your computer that will promptly identify and quarantine an infected download.
Have a look at the answers to these questions:
Where can I watch movies online for free?
Where can I download free movies for my iPod Touch?
What is the best free anti-virus and anti-spyware software?