1. What was your reasoning for running a boot time scan.
2. I rather doubt that they would be slowing down your system, as they are essentially very large compressed files that for the most part will be inert. So they shouldn't be slowing down your system
3. The boot time scan should generate a scan report, from memory I think it is called aswboot.log and would be in the C:\ProgramData\AVAST Software\Avast\log folder, was that where you looked ?
But personally I wouldn't worry about them.
- Decompression Bomb, a file that is highly compressed, which could be very large when decompressed. This used to be a tactic long ago to swamp the system.
The name really is the most dangerous thing about this and I wish they would change it or simply not report it, a real PITA.
These highly compressed files are generally 'archive' files which are inert, don't present an immediate risk until they are unpacked. If you happen to select 'All packers' in your on-demand scans then you are more likely to come across this type of thing. Personally it is a waste of time scanning 'all packers' and that is why it isn't enabled by default.