Corrupted data after 4 viruses

A Windows 98 user suddenly had 4 viruses, Badtrans.B, MTX.EXE, Klez.E, Trojan Horse. I removed them all, then Windows and internet was working normally, but letters & numbers in Word 2000 and Excel files were full of foreign characters and ‘squares’. It’s a Dell PC 2 years old. Can anyone help?