I haven't had a virus in the last ten years, and I'm running Win & NAV.
It scans any executable file when opened/executed, so it should be reasonable safe if your virus definitions are current (in my case I automatically update them once a day).
I don't see a need for a virus check in LW unless you don't trust your current antivirus software, and if so, you should seriously consider upgrading to a better antivirus solution.