The question of the security and correctness of the file.

Approximately August 28, 2016 I downloaded a package of codecs (mega or full). Md5 - I did not check the сhecksum. Were there any problems with the servers at that time and could I download the wrong (damaged or infected) version of file?

The codec pack is clean. There has not been any issue with server.

Why then does the application sometimes fail to respond if I try to open the file in Media Player Classic?

There can be lots of causes for that. Including many external factors.

Start by uninstalling your current version and then installing the latest version.

If the problem still occurs after that, then I need some more information about when the problem occurs, how often, and with what kind of files.

Admin wrote:The codec pack is clean. There has not been any issue with server.

Replaced the term  in the sentence (signature to the checksum). Will your answer be the same?

The files are the server are clean. But I don't know what you have downloaded and from where. You don't seem to even know yourself. I also don't know why you seem to think there is a security issue. Like I said before, if you have a problem, uninstall your current version and use the latest version.

Admin wrote: But I don't know what you have downloaded and from where.

Just in case, I'll explain: I downloaded the links  on the specified date (August 28, 2016) "http://codecguide.com" -> Download -> Download Full (or Mega) ->Mirror 1.  In advance thanks for the answer.

Then the installer was fine.

MPC can fail to respond for many reasons, for example: third party codecs on your system, driver bugs, Windows bugs, damaged files.

It would be desirable to ask last time. Is it possible to check whether everything was normal with the installer from August 18, 2016 to September 8, 2016? I also downloaded and installed through the referenced link ("http://codecguide.com" -> Download -> Download Full (and Mega) ->Mirror 1) to other computers without checking the hash.

The installer checks if files are corrupted during installation and will show an error if that is the case. So if it got damaged due to a download error, it wouldn't have installed.

Why do you keep implying that there must have been an issue? I get the feeling that you are not telling me something.

Thank you. Sometimes servers are attacked by hackers and they (hackers) infect the installation packages. I hope that you have never had this ...    Can I hope so? I do not use Anti-Virus ...
P. S. Can answer briefly.

Never had such problems. The website has many visitors, so it would be detected quickly. The files are frequently scanned with virustotal.com which scans with 61 different virus scanners.