The very popular CCleaner utility from Piriform(owned by Avast) has become a victim of a modification which means that it has been infected with malware from the vendors own site.
It just shows that even relatively well trusted sources of software can become a victim of upgrade/update install hacking.
If you use or have used CCleaner in the past, please ensure that you upgrade the software as soon as possible. The potential attack vector has been removed (bomb deactivated) – but the update will remove the malicious code entirely.
Avast response can be found here: https://blog.avast.com/update-to-the-ccleaner-5.33.1612-security-incident