Proof That Multi-Billion Tech IPOs Aren’t Just for the U.S.

Every company that gives away its product free is getting something in return.

This is true of Avast, a consumer cybersecurity company that plans to sell shares in London in May, joining the healthy wave of mainly U.S.-based technology initial public offerings, such as cloud-storage outfit Dropbox in March.

Avast could be valued at upward...