la fecha del ultimo escaneo no se actualiza, siempre muestra un fecha antigua
Bienvenida Mariana ! Ingles por favor… 
Yes and welcome to forums Mariana23 !
Your language sounds so romantic I must notice, but please post in English since these forums are Technical support only in English language. For many of us English is not our native language, but sure it’s easier to understand and communicate. Not many forum memebers will understand you if you post in your native language. Some of them will understand you without any problems, but still, it would be better to post in English… just because when problem is solved, other users will be able to understand the solution and it can also help them as well in case they have similar problems to deal with… if it’s in Portugese or Spanish only, then it will be much more difficult for eveybody.
I hope you understand this… and WELCOME to best forums ever (at least they used to be) :-\ !
Hasta que puedas hablar inglés, solo algunos de nosotros podrán ayudarte.
La fecha del último escaneo solo se actualiza cuando se usa el scaneo de todos los discos duros.
No se actualiza escogendo el ícono de algunas partes de la ordenadora (ni tampoco si en este ícono coges todo).
La próxima version de avast! debe traher la aclaración: fecha del último escaneo completo de la ordenadora 8)
Translation Please Technical. Thanks 
No, it’s not necessary… It’s the well known problem of the “Date of last scan” posted ad nauseam here is forums.
Next avast! version will have a correction for this: “Date of last full scan”.
Good tech saves the day nice to see your back ;D