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!