Hushmail states Safari has serious security breach and to not access email from it.

After upgrading to os X Mavericks a couple of days ago, I purchased a new Hushmail account and received the warning above. Hushmail stated to refrain from using Safari until the security breach has been patched.

Has anyone else had this problem? Is it for real?

I downloaed Firefox and was going to access Hushmail from that only, but it is inconvenient.