You should not run wallet on Windows. Period. LTC wallet of a friend of mine was robbed by a trojan horse he did not even know he had. Despite having antivirus installed.
Google litecoin wallet trojan windows.
Your friend's problem wasn't windows itself, but downloading and running random files from the interwebz while naively relying on a virus scanner.
Pull your heads out of your asses. No piece of software, be it OS or antivirus, will be able to protect you from yourself.