according to an embodiment , a server system 100 comprises at least a server memory 102 and a server processing unit 101 . typically , the server system comprises a pluralities of memories and of processing units . an electronic device 200 , having a device processing unit 201 and a device memory 202 , allows a user to create and modify a virtual document vd . typically , the electronic device 200 is a computer . the electronic device 200 ( in addition to the means required to the user to interact , e . g . to see and modify , the virtual document , e . g . a keyboard 203 and the screen 204 ) is provided with means 205 allowing connection with the server system 100 . the connection means 205 may be of any kind known , e . g . wired or wireless , that allows to guarantee a connection and an exchange of data between the electronic device 200 and the server system 100 . both the server system 100 and the electronic device 200 are preferably provided with software to implement one or more aspects of the method here discussed . when the user creates a virtual document vd ( or when he opens an already existing virtual document ), the device processing unit 201 set the present method in motion . in particular , the device processing unit 201 may be programmed to start the present method each time a certain application is started on the electronic device 200 ( e . g . each time a word processor is opened ). at subsequent time intervals , the device processing unit 201 encrypts the virtual document vd , and creates an encrypted copy of the virtual document evd ( from now on also referred as “ encrypted copy evd ”). each encrypted copy evd is provided with information relating the time of its creation . typically , the device processing unit 201 does not encrypt directly the virtual document , but it encrypts the content of the virtual document . as an example , considering a virtual document vd that is a plain text , e . g . a “. txt ” file , the encrypted copy evd may be still a plain text document , e . g . another “. txt ” file , where the content of the file has been encrypted . as a result , the “ encryption ” generally does not restrict the possibility of opening the encrypted copy , but prevents understanding of the content of the encrypted copy . in other words , generally , it is not the file of the encrypted copy evd that is encrypted , but it is the content of the encrypted copy that is encrypted . preferably , the content of the virtual document is hashed into one or more hash codes . the encrypted copy evd is thus the list of these hash codes . preferably , the content of the virtual document is logically divided into a plurality of portions , and each portion is hashed into a hash code . as an example , a virtual document containing a text may be logically divided into a plurality of portions , each of the portions corresponding to a paragraph of the text of the virtual document . the encrypted copies evd are then sent to the server system 100 , that analyzes the differences between the various encrypted copies of the same virtual document , to evaluate the activities of the user of such a virtual document . as an example , the server system may receive an encrypted copy evd of a virtual document each 10 minutes . it e . g . receives four encrypted copies evd1 , evd2 , evd3 and evd4 of the virtual document vd . when confronting the first two encrypted copies evd1 - evd2 , the server processing unit 101 notices that no amendments were made in the document . subsequently , from the encrypted copy evd3 , the server processing unit 101 notices that the position of two paragraphs were changed , and that a new paragraph has been added . finally , from the encrypted copy evd3 , it notices that two further paragraphs have been added to the virtual document vd . as mentioned , each encrypted copy evd1 - evd4 is provided with information relating the time of its creation , so that the progress of the activities of the user can be evaluated as a function of time . also each portion may be logically divided into sub - portion , and each sub - portion may be hashed independently from the other . as an example , the hash of the first portion of the virtual document of an encrypted copy may be kjhs80d87as9yuvioy9876vckjhvfa . the hash of the first portion of the virtual document of a subsequent encrypted copy may be kjhs80d87aoeudbqorlo76vckjhvfa . from the comparison of the two encrypted copies , the server processing unit 101 notes not only that the user has amended the first portion of the virtual document , but also that these amendments were carried out only in the central sub - portion of the first portion of the virtual document . the different encrypted copies need not be in different files . as an example , the copies evd1 - evd4 may be in a single file , e . g . : in this case the content of the virtual document is copied in encrypted ( hashed ) form after an indication about the time when the document was copied . together with the encrypted content of the document , the device processing unit may send to the server further information relating the activities of the user on the virtual document . as an example , the device processing unit may record the time actually spent by the user on the virtual document . this may be e . g . done by recording the time wherein the virtual document is an active window on the screen of the computer 200 . also the device processing unit may record the time spent by the user on the virtual document while writing . this may be done e . g . by recording the total time spent by the user pressing keys on the computer 200 while editing the virtual document . as a further information , the device processing unit 201 may provide to the server system 100 the evaluation of the time spent by the user on reviewing the virtual document . this may be done e . g . evaluating the time spent on the virtual document without writing , but moving the pointer and / or by evaluating the scrolling speed of the text on the screen of the computer 200 . also , the device processing unit 201 may record information relating the presence of text ( or other elements ) of the virtual document that are copy / pasted from another source . all these information may be inserted within the encrypted copy of the virtual document evd , or they may be saved elsewhere , e . g . in a separate file on the server . according to an embodiment , all of part of the additional information on the virtual document vd that are gathered by the device processing unit 201 are inserted within the hash code . as an example , considering the hash code of a portion of a virtual document ( e . g . kjhs80d87as9yuvioy9876vckjhvfa ), some characters may be added at the end of the hash code , showing information e . g . about the length of the portion , the time spent by the user for writing the portion , the time spent by the user changing the formatting the portion , the amount of the portion copied by another source . the hash code may e . g . become kjhs80d87as9yuvioy9876vckjhvfajk19i3hju15 . from the characters jkl the server processing unit 101 may infer the number of characters of the portion , from the characters 9i3 the server processing unit 101 may infer the number of minutes spent by the user in writing the portion , from the characters hju the server processing unit 101 may infer the minutes spent by the user changing the formatting of the portion , from the characters 15 the server processing unit may infer the percentage of the portion copied from another source . the server processing unit 101 may be provided in a known way with instruction relating how to manage the information within the hash code . the information contained in the hash code may be different from what mentioned , and in general , it can be any information relating the virtual document vd , and / or the activities of the user on the virtual document vd . thus , when a user opens ( or creates ) a virtual document vd on the electronic device 200 , the device processing unit 201 start to create encrypted virtual copies evd of the virtual document vd at different ( i . e . subsequent ) time intervals . the time intervals may be constant ( e . g . an encrypted virtual copy is created every 10 minutes ), or it may vary , e . g . according to a pre - determined pattern . as mentioned , the wording “ encrypted ” does not imply that the encrypted virtual document ( i . e . the electronic file ) is encrypted , but it refers to the fact that the content of the encrypted virtual document is encrypted . also , there may be a different electronic file for each encrypted copy evd , or they may be stored in a single electronic file . each encrypted copy evd is associated to information relating the time when the encrypted copy evd was created , i . e . the time when the content of the virtual document has been encrypted and written within the encrypted copy evd . the device processing unit 201 stops creating the encrypted virtual copies evd when the virtual document vd is closed on the electronic device 200 . the device processing unit 201 sends the virtual copies evd to the server system 100 via the connection means 205 ( e . g . via a wired or wireless network ), so that they are stored on the server memory 102 . if the connection means 205 can &# 39 ; t reach the server system 100 , the device processing unit 201 stores the virtual copies evd in the device memory 202 . as soon as the connection between the electronic device 200 and the server system 100 is established , the device processing unit 201 sends the encrypted virtual copies evd to the server system 100 . once the server system is provided with the encrypted copies evd of a virtual document vd , the server processing unit 101 starts processing the encrypted copies , in order to produce a report containing the evaluation of the activities of the user on the virtual document . in particular , the server processing unit 101 compares the plurality of different copies one with the other , to evaluate the amendments carried out on the virtual document vd as a function of time . furthermore , the additional information relating the virtual document vd and / or the activities of the user on the virtual document provided by the device processing unit 201 to the server processing unit 101 is evaluated in this step . as mentioned , this information may be e . g . one or more of : the time spent by the user on the virtual document , the time spent by the user on the virtual document while writing , the time spent by the user on reviewing the virtual document , information about the use of material ( e . g . text ) from another source , etc . the processing of all this data is carried out by the server processing unit 101 , which typically has a greater computing power with respect to the device processing unit 201 . as mentioned , the report is generated as a function of objective parameters , that are not affected by the perception of the user . as a result , the report can show a realistic and certified representation of the work done by the user . it is noted that particular reference was made to a virtual document containing only text . the present method may be applied as well to virtual document containing other kinds of material in addition ( or replacement ) of text . the hash function may be in principle applied to any kind of content . as an example , a virtual document may contain three paragraphs of text and an image . the three paragraph may be e . g . hashed as three different portions of the virtual document , while the image may be hashed as the fourth portion of the virtual document .