welcome to the forum.

yhea avast have some problem with that kind of malware but no antivirus program have 100% detection.

malwarebytes is a good program to deal with this kind of infecion.

http://filehippo.com/download_malwarebytes_anti_malware/

if you have the sample of that nalware you can send it in to avast by add the file/s to the chest and upload it from the chest to the avast lab so they can improve there detection.

hope this will do for you

welcome here agian.