Hello, please take a moment to read the following: https://mojang.com/2014/04/heartbleed/
Technic does not use HTTPS for logins (not something we're particularly proud of, I promise), so technically your Platform login would not have been exposed. If you share this password with any other service, especially your email, though, you should change it anyway. And of course, please be sure to change your Mojang password and passwords for basically every other service you use. It is possible that someone, somewhere, knew about this bug before it was announced and could have used it to collect information on your credentials at some point, from any service that uses SSL, which is almost every service on the internet.
Please be safe out there, everyone.