Security is a relative issue and there are several layers of security to consider when using an internet fax service provider. Depending on issues inherent in internet faxing and on providers' specific features, it is then up to you to compare your alternatives as opposed to using a service.
Both for inbound service and for outbound service, there are these issues to consider:
- The internet fax service provider is a third party who is a direct recipient of your faxes or emails. This means that you must trust the provider not to make unwanted use of your faxes. Assuming that internet fax service providers have a commercial interest in retaining their clients, it's quite unlikely that they will make any unwarranted use of your faxes. However, remember that by using a service you are implicitly trusting its provider.
- Your faxes are transported over the public internet as emails. This means that they are as susceptible to interception as regular email. This can be overcome if your provider (1.) lets you upload your public digital ID to their servers for inbound service, so that faxes received for you are encrypted before being forwarded to you, and (2.) publishes their public digital ID for outbound service, so that you can encrypt your emails before sending them through the provider.
- Your faxes may be saved on the provider's servers for your future convenience. Some internet fax service providers let you view your faxes through a web-based interface. This is done for your convenience, so that you can view your faxes after having sent or received them. However, this makes your faxes only as safe from hackers as the provider's servers. This can be overcome if your provider offers an option to keep or to delete your faxes. Remember, that this means that you cannot then view your faxes online.
Remember that in any case, your faxes travel over the public telephone network, and are therefore only as secure as the public telephone network itself.