I had purchased Bit Defender Internet security last year. It was not heavy like quick heal, so the system does not face lag for this antivirus also updates are small so does not require internet too much. Going well I thought it was great antivirus but suddenly I noticed my laptop got affected with trojan so, while I am inserting pendrive containing my data on my friends laptop his anti virus shows trojan found ( He has kaspersky) . But in my system nothing found like trojan after searching using bitdefender. Afterthat I changed my AV to Kaspersky and believe me it was trojan effected. Kaspersky detected over 500 infected files where bit defender could not find any.
So, I will say it does not work at all.