7-zip is a file archiver, similar to .zip or .rar files, it produces .7z files. It is a popular archiving software and it is produced by the developer named Igot Pavlov. However I can not tell you if the specific file you have is save without a file signature (MD5, SHA256, etc...) as long as you get your download from http://www.7-zip.org/ then the file is likely safe. Also you can always scan the file with Webroot to see if it is safe or not :D.

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Also recent versions of Windows have a zip and unzip function built in, so you don't really need third party software to unzip stuff.

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