The computer might be compromised if its physical components have been altered.For example, if a keylogger has been physically installed on the computer, your passwords, personal information, and other data typed on the keyboard could be stored and accessed by someone else, even if you are using Tails.
Use a [[password manager|doc/encryption_and_privacy/manage_passwords]] to paste saved passwords. This way, you don't have to type passwords that might be visible to people or cameras near you.
Other hardware alterations are much more complicated and expensive to install. For an example, see <a href="https://arstechnica.com/tech-policy/2014/05/photos-of-an-nsa-upgrade-factory-show-cisco-router-getting-implant/">Ars Technica: Photos of an NSA “upgrade” factory show Cisco router getting implant</a>.