VBA is functionally rich and extremely flexible but it does have
some important limitations, such as limited support for "callback" functions.
The automation functionality provided by VBA has caused Excel to
become a target for macro viruses. This was a serious problem in the
corporate world until antivirus products began to detect these
viruses. Microsoft belatedly took steps to prevent the misuse by
adding the ability to disable macros completely, to enable macros
when opening a workbook or to trust all macros signed using a
trusted certificate.