Make sure you are downloading from the official source www.7zip.org and NOT www{dot}7zip{dot}com. Someone registered the .com and copied the legitimate one to fake out users in downloading a bad installer.
www.bleepingcomputer.com
Malicious 7-Zip site distributes installer laced with proxy tool
A fake 7-Zip website is distributing a trojanized installer of the popular archiving tool that turns the user's computer into a residential proxy node.