Cognitive theorists believe the disorder to be a result of an underlying belief that other people are unfriendly in combination with a lack of self-awareness. Diagnosis
ICD-10
The World Health Organizations ICD-10 lists paranoid personality disorder under (F60.0). It is a requirement of ICD-10 that a diagnosis of any specific personality disorder also satisfies a set of general personality disorder criteria. It is also pointed out that for different cultures it may be necessary to develop specific sets of criteria with regard to social norms, rules and other obligations.PPD is characterized by at least three of the following symptoms:

excessive sensitivity to setbacks and rebuffs;
tendency to bear grudges persistently (i.e. refusal to forgive insults and injuries or slights);
suspiciousness and a pervasive tendency to distort experience by misconstruing the neutral or friendly actions of others as hostile or contemptuous;
a combative and tenacious sense of self-righteousness out of keeping with the actual situation;
recurrent suspicions, without justification, regarding sexual fidelity of spouse or sexual partner;
tendency to experience excessive self-aggrandizing, manifest in a persistent self-referential attitude;
preoccupation with unsubstantiated "conspiratorial" explanations of events both immediate to the patient and in the world at large.Includes: expansive paranoid, fanatic, querulant and sensitive paranoid personality disorder. Excludes: delusional disorder and schizophrenia. DSM-5
The American Psychiatric Associations DSM-5 has similar criteria for paranoid personality disorder. They require in general the presence of lasting distrust and suspicion of others, interpreting their motives as malevolent, from an early adult age, occurring in a range of situations.
This kind of insecurity leads to overcompensation: compulsive formality, strict social observances and exaggerated displays of assurance.In 1950, Kurt Schneider described the "fanatic psychopaths" and divided them into two categories: the combative type that is very insistent about his false notions and actively quarrelsome, and the eccentric type that is passive, secretive, vulnerable to esoteric sects but nonetheless suspicious about others.The descriptions of Leonhard and Sheperd from the sixties describe paranoid people as overvaluing their abilities and attributing their failure to the ill-will of others; they also mention that their interpersonal relations are disturbed and they are in constant conflict with others.In 1975, Polatin described the paranoid personality as rigid, suspicious, watchful, self-centered and selfish, inwardly hypersensitive but emotionally undemonstrative. However, when there is a difference of opinion, the underlying mistrust, authoritarianism and rage burst through.In the 1980s, paranoid personality disorder received little attention, and when it did receive it, the focus was on its 
potential relationship to paranoid schizophrenia. The most significant contribution of this decade comes from Theodore Millon who divided the features of paranoid personality disorder to four categories:1) behavioral characteristics of vigilance, abrasive irritability and counterattack,
2) complaints indicating oversensitivity, social isolation and mistrust,
3) the dynamics of denying personal insecurities, attributing these to others and self-inflation through grandiose fantasies
4) coping style of detesting dependence and hostile distancing of oneself from others. Controversy
Due to repeated concerns of the validity of PPD and poor empirical evidence, it has been suggested that PPD be removed from the DSM.