According to Testaankoop, the Belgian equivalent of the Consumers' Association, two types of Linksys routers are sending Wi-Fi login details in plaintext

During installation, the router sent several data packets to an Amazon server in the US. These packets contained the configured SSID name and password in clear text, as well as some identification tokens for this network within a broader database and an access token for a user session that could potentially enable a MITM attack.

Linksys has refused to acknowledge/respond to the issue.