It isn't a virus or some sort of FTP compression.
It could be a couple of things going on:
For instance the server is likely running Linux and your desktop is likely running Windows. It is likely that your server and desktop are set to display file size differently.
In some operating systems, file sizes tend to be expressed mebibytes (e.g. 1 GiB = 1,024 ...
If you need to change the URL of a page as it is shown in search engine results, use a server-side 301 redirect. This is the best way to ensure that users and search engines are directed to the correct page. The 301 status code means that a page has permanently moved to a new location.
301 redirects are particularly useful in the following circumstances: