installer.exe is a program which is most likely NOT a virus or malware. So, if installer.exe is on your laptop or desktop computer, it is most likely ok, and will NOT cause problems. Even if your PC is clean, it is still recommended to use a well-known antivirus with a good track record, in order to defend yourself against viruses and malware.
Normally, this program is located in C:\WINDOWS\Temp\opera autoupdate\CProgram Files (x86)Opera\installing\installer.exe.
The MD5 checksum for this file is 23957cec7c21be507f2e52c5cd759081.
This application does NOT operate as a Windows service. This is usually a good sign.
This application uses the Internet to communicate. Today this is expected from a program. For example, most of the programs on your computer check for new updates. In order to do this, Internet communications are required.
This program runs as a 32-bit program. It can not benefit of the entire set of features of current computer CPUs. This is quite normal because the publishers did not bother to upgrade it to 64-bit code.
The description present in the file is Opera Installer.
File version extracted from the file 43.0.2442.991.
Company name Opera Software.
Legal copyright Copyright Opera Software 2017.
installer.exe is digitally signed. Today the large majority of serious software applications are digitally signed.
The digital signature attached to installer.exe verifies as ok. This is most likely a clean, ok program.
Digital certificate name: Opera Software AS
Certificate's issuer name: DigiCert EV Code Signing CA (SHA2)
This application does NOT have a removal routine stored in registry.