Ok so for example i got an older bitcoin core version, way before the header stuff was included. So if i download the latest version, do i have to redownload the blockchain too? Because the blocks got corrupted?
Also i use blockchain.info as a secondary online wallet, do i have to worry when i send or when i receive bitcoins?
If you run the latest core version you're fine.
as for blockchain.info - they did not even identify this issue (read up in this thread) - so it's not save to use them at the moment.