This is the kind of thing that only those targeted for infiltration are likely to be aware of at the time. States still do domestic spying and infiltration of socialist groups, jail them, etc. In the UK, "Spy Cops" is a fairly recent discovery where the UK government had cops join socialist orgs undercover. They befriended people, got involved romantically, even had children before ghosting, having fulfilled their "mission". Organizers of movements end up dead in surprising ways, with odd correlations. A conspicuous number of BLM organizers of Ferguson are now dead and I recommend looking into that.

One thing to consider is that these programs essentially worked, or at least anticommunism won through its various methods, not just terrorists. Europe has no substantial communist movements any longer outside of maybe Greece and Serbia. In most Euro places any inkling is oppressed by the liberal state apparatus and they target small groups that do things like read or protest genocide or help people unionize.

There are places where communist agitation is more active and the state violence and terrorism is greater there. The most active are Maoists like in India and The Philippines and the states there routinely arrest and murder them, generally for siding with indigenous people that want to secure their land against mining and other exploitative interests. Many are martyred for this work.