Windows 8.1 comes with Anti-Malware protection which is Windows Defender. In start, if you search for Windows Defender, you could open it. It is replacement for Microsoft Security Essentials in Windows 8.1 and it will protects same way as Microsoft Security Essentials.
You don't need any additional Anti-Malware protection and you could just use Windows Defender in Windows 8.1 as it protects you against Virus, Worm, Trojan, Spyware, Adware, etc.