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A computer in physical possession of an adversary even briefly may be compromised in BIOS, hardware or software. The computer must not be used to access any accounts or open any password protected files. Wipe the drive. Dispose of the computer.
If files must be recovered, remove the hard drive and use it as an external drive on another computer to copy the files. Removing the drive from the original computer avoids compromised BIOS or hardware. Not booting the original computer's operating system avoids software that might have been installed. This does not protect against you copying infected files to the new computer.