Bitcoin is not 100% secure..
You know yourself that bitcoin prices are very volatile,
may in some time you decrease the value of your money quickly.
The bitcoin it self is very safe for sure, but if you look at online wallets is less much safe this is because online wallets can be hacked.
You can create a paper wallet or use a wallet from the blockchain and make sure you will use multiple wallets.
Online wallets or exchanges of bitcoin is not very safe. Somebody in the service can steal the coins from you.
Yeah, vulnerable to hacker attacks..