We address the problem of pollution attacks in coding based distributed storage systems. In a pollution attack, the adversary maliciously alters some of the stored encoded packets, which results in the incorrect decoding of a large part of the original data upon retrieval. We propose algorithms to detect and recover from such attacks. In contrast to existing approaches to solve this problem, our approach is not based on adding cryptographic checksums or signatures to the encoded packets, and it does not introduce any additional redundancy to the system. The results of our analysis show that our proposed algorithms are suitable for practical systems, especially in wireless sensor networks.