Hello Bogdan,
that is because there is no Anti Virus Plugin for The Bat! at the moment

They have only build in the function. Me for myself am also waiting for a plugin that gets KAV Pro 5.0 to work. Everybody tells you that there is no plugin needed anymore but like the personal version KAV Pro can only tell you in which mail database to find the virus. After that you have a really hard time to find the mail. You will have to delete the mail manually because the database is protected so KAV can not deal with the problem.
I gave it a try with a virus test file last week and it is really a mess.
The Bat suggests that it is imune against viruses but that is not true.
I would also like to have a variety of plugins to choose from for a long time now. And I mean that users should be able to get them right here and not by searching the bat fan sites and receiving 3rd party plugins like it is at the moment with the KAV Pro 4.5 Plugin which is of course outdated.
If I´m not up to date with this plugin matter please correct me but I really think anti virus could be supported much better just like anti spam which is a burning issue on this forum as well

regards
moongate