Using crack or illegal antivirus software is offensive crime under copy right law. Hence I recommend to use licensed Antivirus Software. There are many alternative for home users are available for free. You can use Avast Home basic or Comodo antivirus.
Disadvantages of using cracked version of Anti virus software, When we installed the software program it will try to connect his mother server. Yes we already bypass the key activation but there may be chance of hidden program that connect and mark you on his server as a spammer. Here they can try to test there program without knowing you on your PC (this is my thoughts no any evidences now) that may harm your PC. Other chances of hidden spyware which theft your valuable information. Its a big risk to use such type of software. Be careful and avoid using cracks.
with best regards
Vilas is right there is so many free antivirus like Avast is available or you can use the trail version of any antivirus no need for cracking. Sometimes cracking a antivirus effect your PC in future. Even Kaspersky has also trial version of one month or Avast is also available for 2 years it is also a super antivirus and trusted one no need to crack a antivirus.