In case of problems with Anti Virus software:
Some Anti Virus software packages detect the Stoichiometry add-in as malicious, because it is an executable file that also contains code referring to the Windows Registry. However the file is not malicious, it is a problem that many software developers encounter when posting new software on the internet for download (try e.g. to search Google with the search terms "software developer detection anti virus"...
If you want to check the file "Stoichiometry.exe" for possible virusses, try to upload it to the website Virustotal:
After analyzing the file using the databases of almost all antivirus software, it will indicate which antivirus packages consider this file as suspicious and which consider it as safe. As you can see in the report, well known antivirus packages consider the file as "safe".
In order to use the file, it needs to be indicated as safe in your antivirus package. Most antivirus packages give the possibility (most often in a "Settings" screen) to indicate files as safe or "exceptions" during the scanning process. Type the name of the file (Stoichiometry.exe) in the exception list to stop the warnings.