is it a good idea to store bitcoins in popular online wallets like blockchain.info or coinbase
can these wallets get hacked one day ?
I'd suggest creating multiple wallets at Blockchain and Xapo.
I was in a delusion that Hardcore wallets are better than online versions but they come with drawbacks too. You need to safely store your offline wallet from your family and friends. If you format your Hard Drive or your PC crashes due an accident, you lose your money. Forever!
Store your money in parts on several wallets and each should have a different password of its own. Store private key in your cell phone or an old book etc. You might say that remembering several passwords is too tough for me. The best option is to encrypt your password using MD, md5, sha1,sha5,sha256 etc. Suppose my password is 123 for all the wallets. I encrypt it using all the above hashes. (You can encrypt them easily just google "Encrypt text to sha/md" etc) Thus, you have several passwords by only knowing 1. Even if one of your wallet is hacked, you can still rest assured that you have a backup of 5 more.
Hope it helps