Data corruption problem

IDM started to download the file using one connection because of data corruption when newly received data in several connections did not match the same data downloaded earlier.

IDM started to download the file from the beginning since data was corrupted because newly received data did not match the same data downloaded earlier.

When IDM downloads a file using several connections, IDM requests several bytes more for every file part to match the adjacent file part data which was downloaded by another connection. When IDM resumes a download, it falls back on several bytes and compares the beginning on new data with the end of old data downloaded earlier. When the data does not match, IDM will re-download the non-matching file part from the beginning. When the data does not match in several connections, IDM will start downloading the file from scratch using one connection.

The corruption of data may happen because of the following reasons:

  1. FireWalls, antiviral and other security software control the process of downloading from network and writing data to disks. These programs interfere in opening network connections and in file creation process. When IDM wants to write received data to files, security programs first pass all data through their internal buffers where they scan data for possible viruses. Several FireWalls and some antiviral softwares mix the data of different connections, and thus they mix file parts. For example, several versions of Eset NOD have this problem. When IDM opens several files quickly in one thread, it mixes file descriptors. Also many other cases are known when security programs caused a data corruption. Note that even disabling the security program may not help because they still have their drivers in memory which do this job in background. Users reported successful problem resolution only after uninstalling a security program. Note that IDM cannot in any way bypass a security program when downloading or saving files, and data corruption does not depend on IDM. Many FireWalls and antiviral programs give IDM maximum access rights on downloading and writing to disks during first IDM installation. But after IDM updates, security software may see that IDM executable file has changed and starts to block access or turns on detailed download/write verification without user notification. In this case customers report high CPU load, timeouts, and several customers reported data corruption.
  2. Different "Internet accelerators" or "Video accelerators" may also interfere in a download process. They also may cause the same problems just like security software
  3. Such problems are possible with proxy servers either set in IDM or transparent proxy servers that can be used by your Internet provider. In this case try to change the proxy server, try another Internet provider, or use VPN.
  4. If IDM downloads from the majority of sites without a problem, but has a problem with specific site(s), then the problem is in the site(s). There are sites which send incorrect data on resume, or the site always send files from scratch. In this case please contact site(s) administrators.