Al writes "Rob Lemos reports that Iran's national ISPs seem to have recently gained the ability to filter large quantities of web traffic more effectively. Arbor Networks used data gathered from distributed network sensors to monitor the data going to Iran from the global internet. The firm found that all of the country's providers showed an enormous drop in traffic following the contested June 12 election, then nearly normal traffic patterns until June 26. After that, five of six national ISPs showed an 80 percent drop in traffic for approximately three weeks. The one internal ISP that continues to see significant traffic during those three weeks counts many government ministries among its clientèle. The picture painted by the data is of an ISP that is becoming increasingly skilled in filtering, says Craig Labovitz, chief scientist for Arbor Networks."