Every node maintains its own blockchain. Validity of a blockchain is verified by checking “proof of work” hash.

Hash with certain amount of leading zeroes. Difficulty is adjusted for nowadays personal computers, hence if ACIS miner would start mining and eventually flooding the network, peer has an option to blacklist ofender's blockchain.

This example blockchain includes 2 files:
234bb63c83f40c00052c3eb5a5dbb818a221d91fc01fa94a0877bb2f724d13bd
e8d690d9ebf229740d2bebab36c47d36538402d307750de51fff8506a4acbc42

Filenames are encrypted in desc. File chunks are AES encrypted.

{
  "blocks": [
    {
      "hash": {
        "nounce": 149, 
        "pow": "004e55c40be3041c954b69c39ad4c6d8a5cc134b423abaae9b3607742d4ad16d", 
        "prev": "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", 
        "transactions": "c0aebc60f24e43e953abc3c638b3309391b6e80a877592968b72413471d96c9f"
      }, 
      "index": 0, 
      "transactions": [
        {
          "blockhash": {
            "current": "c0aebc60f24e43e953abc3c638b3309391b6e80a877592968b72413471d96c9f", 
            "prev": "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
          }, 
          "fileadd": {
            "chunks": {
              "array": [
                {
                  "hash": {
                    "chunk": "37450413d8b870a01858033f64bcf7df52c1caf1c59e42eb95adf17865187f49", 
                    "content": "9e737d63121dab2ab7a4871bdceeeaa7456a61a00d0b11f8948edf4ddc4ed703"
                  }, 
                  "part": 0, 
                  "size": 512000, 
                  "tag": "HwADN9GOQimHwWEEE1yR6HX3s52pMOE5sZ7Oijrc9E8k6zSxdHblPILkiskYdIkkltUWvoPF\nOJEGPCaFT0DpuJ3u7HO5gxzYBqrrYqNcPtcPX8+vn0/f+EFH5J48HBIM2J/iIDbe+mdjMzZY\nQ83528mWPyNreu2irWLWt/45YwJf1/cfeJL8+VfompVoZiFiiLoAdy9TinmJlENnssATeChb\nJxzND4BC9DfxHGoBHBM6ENcmZvF4384IVpCpt0MM5nFX12nRHn2i+Le0jp9LtPCeHFdoZ2FA\nCvYtjVAmRB4f6sR8QnWrdzDgAYNLczHCKJKAoL1u3Lb2phS3XoLIPg==\n"
                }, 
                {
                  "hash": {
                    "chunk": "eb1eacb380a4e56e3b5d8b20633c787d5e0de9c2b4d945d2fd2bc24d6c2997e1", 
                    "content": "87e8fa7bdf845177b8d7a854e8160ed0bae5409258b37dd3ececb01d478f2f15"
                  }, 
                  "part": 1, 
                  "size": 512000, 
                  "tag": "rYXIg7CFjacl4TykojVFsNSSWQMErF8LI9ocPsrjd8wcpcOQes3VPbkinwTmlXhdUOaJmecq\niIQ/bHy8Zwrybo7UJyXj4WdCY09pykxbOxP7ZmFjraidJ1RZb9u2+G+wCB2qxDUzW/jWAUfT\nKuxETHT6+OJjqmNk8qRwoyiRYsZNIXFxqfTsahKo3MkkVdqoyZUzfB2h0nJuDXR9YG2aBZg1\nDYLu9ukco8E7nVYQqryQBbcVu4wiT0uiHrtiUvUBBFlb+vEploHsXZjNIfnj1LRHha79DZfr\neTWF2RB1cgp6EQjO1MpTm0UTfEoPV3eQLDrrWmeKR8ZJF3nJD838dw==\n"
                }, 
                {
                  "hash": {
                    "chunk": "95233dc08f69d14065e55d7c5e7478ebfed6d8a25e97d19aea1b5e25e3234e63", 
                    "content": "beac6115c3d3cf584a9085112f4f08f57343cd9ed7ba3b9e4ccde01fe3841c15"
                  }, 
                  "part": 2, 
                  "size": 24576, 
                  "tag": "ARgtJVYNsczeT6yGLcLB9qec9KFR8Q3rmT+74Agw4En3fHoULIqQzCAOz1jHn1e+umZ+E3ED\nlTuACFaQ5NA2TyjmupTWHFk1ziW1tP/SJyamKNub9SMsfwlTe19z1jNuN1/Drhwul7dMbCcS\nKztiUu2j+N1zxFWOUoCKGpZi9RZxtzSdPwiAxIOtUKHdTbMcyIg/tfsrAy5Cc9NjF/0XGunv\nvXceSqVlJT5P+V/0mVaCZbHDhrdBPUkzW/EJa2jCc+goIs5tFT2keZHFUZLkBvY9tdnBECKU\noMfEg+GxaaEDawsWO+6awHz+GpHTNfYEMumz8HvzbeJPZDP/Q6OCMA==\n"
                }
              ], 
              "hash": "234bb63c83f40c00052c3eb5a5dbb818a221d91fc01fa94a0877bb2f724d13bd"
            }, 
            "hash": "ea21e972fb60a3a2066544b6834a2d98ae3134c3f9a92eec1dcac52e84d2698b", 
            "meta": {
              "desc": "DpzfB0jqWdOeE5oOAX1x6mb8e7thAnW/TdG0utgkh4DSnSTzH0Imgk3YXXsMzZWWaVpjWVuY\ndeS2zT38jMZoMQEL2fcQp+gREnQJl8pBXJPye1Ir8k/CsMpL2sPyEmfogyWSV7kuoTbAwwwJ\ndfvB1302dP00yt4lVMYye8IlBKCH6JZRG+HFAlWKKZDAHz638n7z2Y9udhm3qVLXeN5K5Ycp\nPfFi/yNZsgteCq6LybMXFYLtLHXDj4ur82bnf2580uQtWz5rl2kCfY4jAIdHCpatca/2axRT\ne+VohU+IjyQQ73tFJchsQJ8wgPrE1exAvYPXxTiURxNuNfzUt3Gr0A==\n", 
              "hash": "365e751f163409a41a4d15db9544a766a253b41d63b4697cad47f6cb79496e4d", 
              "name": "234bb63c83f40c00052c3eb5a5dbb818a221d91fc01fa94a0877bb2f724d13bd", 
              "size": 1048576
            }, 
            "pubkeyhash": "114b48af17746fba6e2f996f97c0d72656eacf72300788d41fd5cf529b0ffd74"
          }, 
          "hash": "9da2cede2830507967a071a51bd8c90b4c2eb77b806c07c63f128d1ac72cd274", 
          "timestamp": 100, 
          "type": 0, 
          "version": 1
        }
      ]
    }, 
    {
      "hash": {
        "nounce": 17, 
        "pow": "00a77438347aca324b8fcd2a0485d2ecbe67d12b100f07842e17d1c732741493", 
        "prev": "004e55c40be3041c954b69c39ad4c6d8a5cc134b423abaae9b3607742d4ad16d", 
        "transactions": "e503b8e159d9abc94e83c6fa49c452aeb1ff25f35555757e827a666251211034"
      }, 
      "index": 0, 
      "transactions": [
        {
          "blockhash": {
            "current": "e503b8e159d9abc94e83c6fa49c452aeb1ff25f35555757e827a666251211034", 
            "prev": "004e55c40be3041c954b69c39ad4c6d8a5cc134b423abaae9b3607742d4ad16d"
          }, 
          "fileadd": {
            "chunks": {
              "array": [
                {
                  "hash": {
                    "chunk": "b76999e6df3fd97cde4b0bdb4f9ca1fec72d49a648368b4cbf89909736f510f4", 
                    "content": "bf031cb3c335cdcd148d75edb937a4330caee01b6d7c87df51fcdbc4ccf227db"
                  }, 
                  "part": 0, 
                  "size": 512000, 
                  "tag": "dU511y8WY6HNHx5yFHTNXzxKdpzJxr7GNpixAe02agYpAm/mV+dG5VkjYXVX0HZsR7i20lcC\n6C0TYhvoUOoY4Vv5hImPKB6DwRpykl6YWv+H2SbJ7pZ6PrjVVDDqsJPm9bEWUGxRdByl4G0u\n3+dNeA0uTP7tlCcHYS5Hxci7ciypnB6wbyk51Q4IEBAbZNuIdI9VSs2Ao1okeo/LAZFcNJC/\nm85YvqQ5t3XGAV4Wfejxs3sghFGgyL8aTfD2XLKwkIBVu1KHGITG/VZoDPJrwVemySEknol+\n6bimcUFH8Io5jtD3GHbHtLZah/tUnUSQjpLX8qd0pqrU1y03wgrFdg==\n"
                }, 
                {
                  "hash": {
                    "chunk": "00d698a84d59e7b6685b6317752573ea20532f63d3e23d9f69a38ad1af85001b", 
                    "content": "ecb9b9dec8adf1eb31969efd27142761b13fc6c947785166a8d9d98edef15512"
                  }, 
                  "part": 1, 
                  "size": 512000, 
                  "tag": "s2WCThYSrSGzWrjAZgo4REaA2f/ZxY25ijB3Va0nnSlNsk7kCPmv7nT9V8rkpQrJde5SGSGm\nYWFgo0ysm2aMAAR+TznfZXnUDU7YrzFa/uGxE4mNiHyuWSNVgXOpt+dAbDJHoKyWfkafeOS5\namrXudPnBVa6be/zEgb/b9+SyCalJIPTSd3jAorbNWrgf+3oeprxwQenvXLDck1Vr3EABdll\nAd+8IZApv/SopcQNsxJ1oLZDzlphSS5bEPUj6pcNM1fkvOZ8D7nfkVXrTxYc7urf/aSFt51S\nrcws6s7ah2Sn40CdEO6Osh7ytYX34KH+0jBjEXWSOp3efMbujSjmdw==\n"
                }, 
                {
                  "hash": {
                    "chunk": "4a5fa125dd32b524184eecba401b91c3c6191312a312368cfb2447a1532b9a13", 
                    "content": "8ecd5c12f9521bcca66eb0ec3a01171c518be0aaf55d579860ee6f2801ea8077"
                  }, 
                  "part": 2, 
                  "size": 24576, 
                  "tag": "tvmZfbPJE8jiyJyv0FIZCqXdlC7EUlVWwjLBzcqgl5XXdzsHImShtuDk3WS92UYVnZ2F7tCH\nhsKjtIp+bDUTueJX+qDF4bGptd74C2AKEgKwlYimO7g0HAmYjU8sBH4E+++2E8z4UWT3/ptS\nQfe8Yov50bhlBJBfX1nCOkLY3Gm+UYJMSwW5BTqgNYqXgaVHllldenhCFX/JR1tSkFLkD0hX\nCEdNggzkjrQPO3jMpen4OBTpr7Dx+6r7W4ePmmM2U2LOa8KNxxBUTncmGj3lvsirrtJedxCN\nEe+Lcev7Hzhhjjp3eP3fEZYHO+aocaXAnwAAjtNPLJ0f2t1pzz80uA==\n"
                }
              ], 
              "hash": "e8d690d9ebf229740d2bebab36c47d36538402d307750de51fff8506a4acbc42"
            }, 
            "hash": "c2409f0c62c3b3caeb572b4f0ef6a44d430823ea2ca12fb48e869d2e317e2187", 
            "meta": {
              "desc": "anAvZM0G4AR7hptrVuIrLey/eLlEJ4tHXElXRLOvIzAMd+R/1oaM5mavaND1Kkkjse3Wtuob\n+mFEeNYrwVpRbgCIs1KwakiFrWVbaLR6r0fL6Ln3A4IeH/yfF48VIOnazgELMROBaQisldvT\nU8L8SH/h/HrHCW3zIZ37xqXYPXaPbRN7qL/gb0/S7XgZ6fQqKddXPyxGnLNi1g0uZdGooYkc\n2UX04p7kbKrTY+P/wI1Xj5BhtTDP/M+rR7B2eSCiQbVj8z5q0Ur4gFimru5jii6G8g0PRCRB\nnX6ECGmggYWt+JWyb+gGaoa/OeCdYGjvbhJz6rXBm7kB87PmgJkCjg==\n", 
              "hash": "af00d25362f008c3197bfefc8b38e7b4f8314ffea9c7df00b08188ec4ecb19e8", 
              "name": "e8d690d9ebf229740d2bebab36c47d36538402d307750de51fff8506a4acbc42", 
              "size": 1048576
            }, 
            "pubkeyhash": "114b48af17746fba6e2f996f97c0d72656eacf72300788d41fd5cf529b0ffd74"
          }, 
          "hash": "6e5acbd32700ac68b79ac88630592e80fc8aad64a7a52d85daa2c645760050c7", 
          "timestamp": 100, 
          "type": 0, 
          "version": 1
        }
      ]
    }
  ]
}