Microsoft Excel 97 and 2000 allows an attacker to execute arbitrary commands by specifying a malicious .dll using the Register.ID function, aka the "Excel REGISTER.ID Function" vulnerability.
https://exchange.xforce.ibmcloud.com/vulnerabilities/5016
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2000/ms00-051
http://www.securityfocus.com/templates/archive.pike?list=1&msg=396B3F8F.9244D290%40nat.bg