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.
Try to keep your computer in a safe location. Hardware alterations are more likely on public computers, in internet cafés or libraries, and on desktop computers, where a device is easier to hide.
Use the [[screen keyboard|doc/first_steps/accessibility#keyboard]], if you are using a public computer or worry that the computer might have a keylogger.
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>.