Questions

You can't.
but you can only make yourself and your data much safER by following general rules and measures - some of those are:

# make your passwords secure - long and special [+more]
# do not use the same password for everything
# change your passwords often, especially email
# when logging and paying make sure the connection is secure (https)

# use Webmail instead of a local mail program, so that malware stays on the server, where you can easily scan and disinfect it
# to know where an email really comes from look at the header [+more]
# delete email accounts no longer used, do not set up accounts like: test
# never reply to spam
# never open attachments unless you are sure where they come from
# never follow given links unless you have a good reason for it
# do not display your email address on your site

# do not download software unless sure of the source - check site address
# if you use free software (Wordpress etc) keep it updated

# do not use your computer as Administrator, but as a normal User