For those not so familiar with a bitcoin buying and security.
Most people buy bitcoin on coinbasepro, or kraken. (commonly referred to as exchanges)
There are other, bigger exchanges, that cater more to the Asian people.
To buy bitcoin, you join your exchange of choice, just like joining a bookie firm.
After depositing, you then buy bitcoin(think minimum transaction £20)
After buying you will now have 2 balances( one for unspent money, and one for your bitcoin)
In the past some exchanges have been hacked, and people have lost their coins, nowadays things are different, Coinbase exchange are planning to float with a valuation of 75 billion dollars, which if floated in the UK would make it one of the top 10 ftse company's. So fair to say leaving your coins there should be pretty safe.
However the idea of bitcoin is to be your own boss of your finances, and beholden to no company or entity. So most people get their own wallet and transfer the coins from the exchange to their own wallet.
if people are interested I will explain this step to your own wallet(where the guy with 7002 has come unstuck)