Sorry but the over dramatic headline “Getting DCOM and LSASS exploit alerts: Probably you are infected” is false, it doesn’t mean you are probably infected, it means nothing more that an attempt has been made to use those exploits to gain access to your system, nothing more nothing less.

DCOM/LSASS Attacks are speculative, not targeted and tries to exploit a vulnerability in out of date OS, if your OS is up to date then you aren’t vulnerable to the exploit. That doesn’t stop them (usually someone from the same ISP with an infected computer, though not exclusively) trying to see if it can infect others.

Your firewall should be the first line of defence in this, but avast also monitors common attack ports using the Network Shield, ideally the firewall should block it and avast wouldn’t know about it, but for whatever reason avast is first in line over your firewall.

What is your firewall ?

If the infection was inside your system it would be trying to get out not in and would usually present itself as an avast alert blocking URL:MAL and from an internal process, svchost.exe, etc. Your firewall (depending on which) should also be blocking unauthorised outbound connections.