Hi there,
Please note that BullGuard does not rely only on the BitDefender's scanning engine.
We are also using a second scanning engine (mostly for Behavioral and On Access detection) and 3 sets of definitions, from which one is "home made".
The Safe Browsing and Spamfilter plugins include technologies from several world leaders in those fields, such as Commtouch ( adopted by Google and many others).
The Firewall module is created by Agnitum, and it is also used by Comodo and Kaspersky, whilst the Vulnerability scanner (the ex Inspector) was developed with Secunia.
As a conclusion, BullGuard Internet Security uses the best technologies available for each plugin in order to provide the ultimate protection.
Hope this answers you question
Cheers!