HTTP Basic authentication not working anymore for jira.atlassian.com REST API

We were using jira.atlassian.com REST API to load some test JIRA data in our eazyBI reporting application and we were using REST API with HTTP Basic authentication (as otherwise some APIs like "user" failed with 401 Unauthorized error) and using our jira.atlassian.com username and password. At least still on January 30, 2015 it was working.

But couple days ago we discovered that simple https://jira.atlassian.com/rest/api/latest/serverInfo with my username and password in HTTP Basic authentication header returns 403 Forbidden response.

If I try another Atlassian JIRA site, for example, https://ecosystem.atlassian.net/rest/api/latest/serverInfo with HTTP Basic authentication then it still works.

What has changed in jira.atlassian.com authentication in recent weeks and why Basic authentication is not working anymore?