Spam is sent from my home PC, how to quickly detect a virus?

Question

Malware

Hello!
There is a local internet provider. Each subscriber has an external "white" IP address. If mail spam starts coming from the subscriber's IP, the provider temporarily disables it (the provider, apparently, receives a claim from the Composite Blocking List, or something like that).
Often friends ask for help with this infection. Struggling with this computer run CureIT, then Kaspersky LiveCD. This takes a lot of time, and it's not a fact that scanners will find a spam bot.
Interested in an efficient and fast way to calculate a virus on a computer for its subsequent removal.
Is it possible to detect a spam bot by network activity? Traffic on port 25, for example. Or a similar subtle approach?

Answer 1

In theory, some firewalls can show a process that interacts with the network on a specific port. But here it may turn out that the firewall and AV installed after infection will no longer work correctly, hiding such activity.

Answer 2

Look what resource opens the 25th port. Set audit to this port.