Thanks for your suggestions.
I've found roughly ten "80" in the four strings. I then copied the following 64 characters in a hex -> base58check converter to obtain the corresponding wif private key and imported the results into a blockchain.info wallet. All the corresponding addresses are completely empty.
Could these strings be generated from a brainwallet dump or something?
Does somebody know if electrum or multibit generate hex encoded backups?
Probably the answer is just behind the corner, but I tried to find infos online without luck for a few days now!
A private key can have two addresses one for the compressed public key and one for the uncompressed public key. Compressed WIF private keys start with L or K while uncompressed ones start with 5. Easy way to get all the possible combos is to enter the private key into bitaddress.org's wallet details tab.