7zip is almost always used to secretly install malicious software and also spyware and adware, if you go to many sites that are filled with ads as well as download managers they almost always have a link to install 7zip, many times if you click that link 7zip will be installed while also being bundled with some type of adware, packaged up spyware, or even trojans and viruses. If you really need to download 7zip you should only download it from the trusted developer's location which is 7-zip.org, or which may redirect you to download it from sourceforge.net. Sourceforge.net also is an ad-fueled site, so I try to avoid it, but as long as you are careful to not just download programs from random links on the internet, and you only download files and applications from their original websites you will be much safer. I would usually tell you to compare the MD5 or SHA1 hash of the applications with the hash that their developer has offered as a comparison, but I have not been able to find the original hash of 7-zip, therefore I try to avoid 7zip and instead use a more reputable program like winzip, which can open 7zip files I believe. Just because software is open source does not mean it is safe, as open source programs are often used to package malware and spyware. I am sure the 7zip EULA is ambiguous because the author of the program needs to use any method available to make money including re-packaging his software with AD-bundlers and opencandy type of revenue generators. Sorry for the long reply, just be careful.
