Zersetzung is the term used for a scientifically developed set of tactics used by the Stasi (East German security service/political police) to silence dissidents and political opponents outside East Germany.

Stasi Emblem

The goal of Zersetzung is the fragmentation, paralysis, disorganization, and isolation of the hostile and negative forces, in order to preventatively impede the hostile and negative activities, to largely restrict, or to totally avert them, and if applicable to prepare the ground for a political and ideological reestablishment.
Ministry for Security of State, Dictionary of political and operational work, entry Zersetzung: Ministerium für Staatssicherheit (Hrsg.): Wörterbuch zur politisch-operativen Arbeit, 2. Auflage (1985), Stichwort: „Zersetzung“, GVS JHS 001-400/81

This technique has been referred to as "no touch torture", or as Gieseke puts it, "Quiet Terror"

its aim lay explicitly in “breaking” the person. This had profound psychological consequences such as anxiety and paranoia.
Neuendorf, (2017). Surveillance and Control: An Ethnographic Study of the Legacy of the Stasi and its impact on wellbeing. Thesis. University College London.

In fact, the tactic is meant to mimic the effects of mental disease, so that people reporting such attacks upon them may be considered as paranoid by others, especially their social support relationships!

Methodology

The basis for attacks against individuals is operational psychology

This involved the application of principles of social and clinical psychology and their deliberate misuse.
Neuendorf, Surveillance and Control: An Ethnographic Study of the Legacy of the Stasi and its impact on wellbeing

• Covert entry into homes and subtly manipulating the contents – moving furniture, altering the timing of an alarm, removing pictures from walls or replacing one variety of tea with another.
• Releasing pests (mice and snakes) into the house
• Returning items from the trash to the home
• Mysterious phone calls
• Un-ordered deliveries
• Other forms of gaslighting
• Property damage
• Intentionally incorrect medical treatment
• Smear campaigns
• Spreading rumors
• Group stalking Reddit devoted to the topic
• Sending falsified compromising photos or documents to the victim's family
• Referencing topics discussed in tapped phone calls
• Causing personal or occupational failures
• Family members were used as leverage against targets

the Stasi often used a method which was really diabolic. It was called Zersetzung, and it's described in another guideline. The word is difficult to translate because it means originally "biodegradation." But actually, it's a quite accurate description. The goal was to destroy secretly the self-confidence of people, for example by damaging their reputation, by organizing failures in their work, and by destroying their personal relationships. Considering this, East Germany was a very modern dictatorship. The Stasi didn't try to arrest every dissident. It preferred to paralyze them, and it could do so because it had access to so much personal information and to so many institutions.
Hubertus Knabe: The dark secrets of a surveillance state, TED Salon, Berlin, 2014

Surveillance of the society as a whole provided two benefits to the Stasi; first it identified targets, and second, by collecting every bit of information possible...

IM were engaged in the amassing of vast amounts of often seemingly trivial pieces of information which could potentially be used in the operative Zersetzung of the enemy
(Miller, 1997)

Targeting

The method was used against dissidents both as individuals and in groups; it was also used against foreign targets. In fact, as the East German government moved from open physical brutality to silence opposition, it turned to this technique which had previously been used as a covert tactic outside east Germany ( Die Methoden der Stasi).

this changed during the 1970s when the GDR became more interested in gaining a positive international image, and the repression of activists became more subtle.
Stasi Tactics – Zersetzung

I wonder if it's worse to get worked over repeatedly, than to be the subject of long term psychological attack...

The fact that psychological expertise and deceptive measures like decomposition (Zersetzung, a hidden psychological destruction of the subject) came to be applied, as well as the sheer number of operative procedures, back this thesis of a second Stasi phase beginning in the mid-1970s.
The Stasi at Home and Abroad Domestic Order and Foreign Intelligence

Selection of targets was mainly done on socialist grounds.

“Zersetzung”was to destabilise the personality of those who had undesirable convictions and who were deemed as opponents of Socialism", employing psychological "dissolution",
(Neuendorf, 2017)

Targeting took into account the amount of influence that Western nations could bring to bear to protect a target, but that influence could not prevent the application of Zersetzung.

Elaborate Zersetzung measures were presumably used on internal opposition groups, as well as on groups of emigration applicants. The more active a "hostile-negative" person was and the more protected from prosecution by the Western media and church, the more extensive the measures taken against him. Less elaborate standard measures were probably used in most operational cases—between 1985 and 1988, the MIS carried out an average of 4,500 to 5,000 operational cases per year—and most likely formed a part of the 20,000 operational person controls carried out annually.
Gieseke, J. (2014)a.

And that influence was also one of those things that the Stasi were looking to counter...

A third priority was containment and control of all kinds of Western influence, so-called political-ideological diversion
(or PID)
Gieseke, J. (2014)b. The Stasi and East German Society: Some Remarks on Current Research. GHI Bulletin Supplement, 9
A note on this article - there is a good discussion of informants in East German society in this article

Development of the technique

By 1958, The Stasi had become so proficient in psyops they began to operate independent of KGB control (Solbrig, 2017). The methods of Zersetzung were developed at the Stasi College of Law (Juristische Hochschule der Staatssicherheit)

Terminology

User 204.96.25.223 on the Wiki Talk page makes the following points about the use of the word

• The accusation of Zersetzung itself: the accused is somehow "undermining" our repressive political or military efforts.
• The methods (Operative Vorgänge) of Zersetzung applied against the accused: all the family, friendship, professional, and supportive relationships of the accused are "disintegrated"

And I will point out that the term Zersetzung had it's origins in Nazi Germany, the concept was expanded and refined by the Stasi.

Other uses

Seclusion and isolation of "the other" is a fairly common social attack mode. However, the Stasi's engineered methods certainly took this to another level.

There is also a good deal of comparison between Zersetzung and some COINTELPRO methods. That is certainly worth a post at a further date. MI6 and the CSIS have also been accused of these psyops. The East Germans were not the only ones who have used these methods! It is probable that the Deep State uses the tactics, and there are suggestions that some companies have used the tactics. It is certain that the left has organized internet lynch mobs.

In fact, a modern accounting of Zersetzung could include

Image Source - Zersetzen

There is always hope

But it’s worth mentioning that, in our assessment, the grassroots opposition movements made the biggest contribution to the revolution that started in East Germany in autumn 1989 – despite the horrifying levels of repression and surveillance that they had faced for decades. Quite simply, the Stasi failed to predict the events of that year, and once things had started their Zersetzung tactics became ineffective.
Stasi Tactics – Zersetzung

I will say that the more "targets" a hostile organization has to deal with, the less effective that Zersetzung becomes. In addition, people who are active against possible users of the technique need to be aware of the the tactics, and be ready to counter or to endure them.

This certainly means taking a second look at any rumors or accusations made against allies; or even putting non-critical issues aside until after the activits' goals have been accomplished.

References and Suggested Reading:

Die Methoden der Stasi

Gieseke, J. (2014)a. The History of the Stasi: East Germany’s Secret Police, 1945-1990. Berghahn Books.

Gieseke, J. (2014)b. The Stasi and East German Society: Some Remarks on Current Research. GHI Bulletin Supplement, 9, 59–72. https://www.ghi-dc.org/fileadmin/user_upload/GHI_Washington/Publications/Supplements/Supplement_9/bu-supp9_059.pdf

Hubertus Knabe: The dark secrets of a surveillance state, TED Salon, Berlin, 2014

Miller, B. (1997). The Stasi legacy: the case of the Inoffizielle Mitarbeiter (PhD Thesis). University of Glasgow.

Ministry for Security of State, Dictionary of political and operational work, entry Zersetzung: Ministerium für Staatssicherheit (Hrsg.): Wörterbuch zur politisch-operativen Arbeit, 2. Auflage (1985), Stichwort: „Zersetzung“, GVS JHS 001-400/81
I am unable to locate a copy at this time, quote taken from Wikipedia

Neuendorf, (2017). Surveillance and Control: An Ethnographic Study of the Legacy of the Stasi and its impact on wellbeing. Thesis. University College London.

Operativer Vorgang, in German...English translation

Solbrig, J. H.(2017). Stasi Brainwashing in the GDR 1957-1990.. Thesis. University of New Orleans

Spiekermann, U. (ed)(2014). The Stasi at Home and Abroad: Domestic Order and Foreign Intelligence. GHI, German Historical Institute. Google Books

Stasi Tactics – Zersetzung

Wikipedia - Zersetzung

Zersetzen