The Ğ1 currency is based on blockchain technology

A blockchain can be described as an encrypted immutable ledger.

Ğ1 developers chose this technology because it has a lot of advantages:

• Immutable transactions (the transactions that make up the ledger cannot be changed or altered in any way).
  
• No centralised organisation can control the network nor the money system. 
• If users choose long and complex enough identification phrase and password, not only is that particular users account/wallet far more secure, but the whole network benefits from such security measures. This is the case in particular when a new G1 co-creator account is being created. We strongly advise that a new 'member/co-creator account' is set up, instead of changing ones existing 'simple wallet' into a co-creator account. This allows the user to make sure they create a strong identifier and password. Between 35 - 50 characters is recommended. Using a phrase or song lyrics etc., is a helpful method. This hyper security focused approach is mostly oriented towards the co-creator accounts, as these are the ones that daily create new currency in the form of the universal dividend (UD). These accounts also have the option to certify other G1 co-creators, as well as G1 newcomers. If a nefarious actor was able to 'hack' into a co-creator account (that didn't have sufficiently strong identifier and password), they would have the ability to certify other accounts (which could be self created), which could greatly jeopardise the whole network. The distance rule within the Web of Trust is designed to mitigate such attacks on the network, but it is still highly recommended to create a strong identifier / password combination.

[note Hugo] I removed "Low energy cost." because it's not a reason of the choice. The whole answer is a bit off-topic. We should define the different aspects of security which is a broad topic before answering the question