You cannot just check suspicious documents such as e-mail attachments with the help of locally installed anti-virus software, but also by using an online service – convenient, but also risky.
In the age of phishing, e-mail attachments and other files copied to your device from external sources should always be verified before opening, since documents of unknown origin, like supposed invoices or applications, frequently contain malware.
If it is not possible to clearly establish who sent a document, checks using a virus scanner can help identify risky files. Many users use online services like Google’s VirusTotal to do so. Some e-mail software or platforms even allow for the use of such scanning services directly from your e-mail facility, so that you don’t have to store any attachments on your own system beforehand at all. That’s convenient and could add another level of security.
However, Internet virus scanning services have one major disadvantage: They usually store all files uploaded and frequently even pass them on to partner services. Such an approach is a basic necessity for the virus scanner to be able to continuously keep “training” it to recognise malware, so that ideally, it is always up to date. Most scan services advise you of this fact by way of a warning message.
The problem is though that such scanners often don’t provide sufficient data protection for users – uploaded data can sometimes be found and accessed by other users even months later. If uploaded files contain third party data worthy of protection, users might even commit an offence under Swiss data protection laws when uploading to any such platforms, which are generally located abroad.
In addition, online services can only check files which are actually uploaded, not those which for instance are copied to your machine by inserting an USB stick, or any files downloaded from a website.
You should therefore use online virus scanners as an additional tool only next to anti-virus software or app installed locally on your device, and exclusively for documents of which you are certain that they don’t contain any sensitive data. Online services cannot replace local anti-virus software.