I noticed a drwebd service running on my linux server, but I thought one had to pay extra for this. Is this some sort of buggy daemon running on the background?

This is part of powerpack - I think - however I have always found it to be poor - didn't stop half the viruses.

You get a 15 mailbox license for free with powerpack to basically try it out so you can decide whether to purchase the full license for the server.

Personally, I'd prefer they either give the full license with the powerpack or give us the option to tie the icon into another 3rd party application like clamav because its misleading to customers.