I received a nice email with a very good question from Mehdy Mohajery. It is not the first time I am asked the same question. This time I am documenting the answer I always give. Question: I saw you profile on linkedin.com just tonight , and I noticed that you are specialist in both p2p systems and designing security systems. that encouraged me to ask a question from you. As you know, nowadays a lot of viruses are being distributed via p2p networks like KAD & EDonkey. If an anti virus vendor like avira could provide a plug-in for a major p2p2 client (emule) to detect viruses before downloading by their FileID (MD4 Hash) , then a major part of virus traffic on p2p networks can be eliminated. So why nobody on security industry seems to care about securing p2p networks with this method? should I download every piece of scrap to know if it’s infected? I like to know your opinion about this. Dear Mehdy Mohajery, There are several reasons why nobody adds an AV for the P2P programs: 1. Having in mind the “free of charge” nature of the P2P networks, nobody will pay for an Antivirus program….