There are many system to safest way to keep bitcoins . If you use blockchain wallet that is a very safest for keep a bitcoin but you must turn on 2Fa verification . When you use 2Fa or google verification code no one can login your account . When you wan to login you can get a again and again new code then you put those code on your browser then you can login your account. This system is very effective for safest way to keep bitcoins.