R. v. Samuels, 2013 ONCA 551:
 Evidence may be admissible for one purpose but inadmissible for another. Where the evidence relates to conduct that is extrinsic to the charges before the court, it may be irrelevant and inadmissible if used for one purpose, but relevant and admissible if used for another. The trial judge is required, as he did here, to weigh and balance the evidence to determine if the prejudicial effect related to the forbidden purpose outweighs its probative value for the proper purpose.
 The courts have observed in cases such as R. v. D. (L.E.),  2 S.C.R. 111, at pp. 127-128 and R. v. J.A.T. 2012 ONCA 177, 288 C.C.C. (3d) 1, at para. 52, that evidence of such extrinsic misconduct carries three particular risks:
a. the jury may conclude that the accused is a "bad person" and convict on the basis of propensity reasoning that he/she is likely guilty of the offence charged;
b. the jury may seek to punish the accused for past misconduct or for conduct unrelated to the offence; and
c. the jury may be confused, and their attention may be deflected by the analysis of the misconduct.
 Courts have frequently stressed the need to "inoculate" the jury against the risks of becoming side-tracked by such impermissible reasoning. For example, in D. (L.E.), Sopinka J., writing for the majority, observed at pp. 128-129:
In a case in which similar fact evidence is admitted, the trial judge should charge the jury in a manner that will minimize as far as possible the dangers referred to above. The jury should be instructed that if it accepts the evidence of the similar acts, that evidence is relevant for the limited purpose for which it was admitted. The jury must be specifically warned that it is not to rely on the evidence as proof that the accused is the sort of person who would commit the offence charged and on that basis infer that the accused is, in fact, guilty of the offence charged.
In the instant case, the trial judge gave the jury no such warning. The similar fact evidence was treated simply as part of the whole body of evidence on which the jury was to determine innocence or guilt. The purpose of the admission of the evidence was not identified and its use was not limited, although the trial judge advised the jury at the time the evidence was admitted that he would give instructions as to the use that could be made of it. Furthermore, the jury members were not warned that they were not to engage in the prohibited line of reasoning to which I have referred. I conclude, therefore, that the charge to the jury was not adequate.
 In J.A.T., Watt J.A. explained the elements of a jury instruction where evidence of extrinsic misconduct has been admitted at para. 53:
Where evidence of extrinsic misconduct is admitted exceptionally in a criminal jury trial, the chief work of mid-trial and final instructions is prophylactic: to confine jury use of this evidence to its permitted purpose and to abjure prohibited reasoning: B. (F.F.), at pp. 707-708 and 733-735. These limiting instructions, whether given as mid-trials or as finals, should contain three elements:
i. a description of the evidence to which the instruction applies;
ii. a positive instruction advising the jury about the use they may make of the evidence (the permitted use); and
iii. a negative instruction directing the jury about the use they must not make of the evidence (the prohibited use).
 It is well settled that this kind of instruction is not confined to cases of similar fact evidence and is required in all cases "where the dangers associated with 'bad personhood' reasoning exist": R. v. B.(C.) (2003), 171 C.C.C. (3d) 159 (Ont. C.A.), at para. 25. The same point was recently made by this court in R. v. Chamot, 2012 ONCA 903, 296 C.C.C. (3d) 91, at paras. 62-63:
The jurisprudence is clear that when there is a real risk that evidence properly admitted for one purpose could be used by the jury for an improper purpose, the trial judge must caution against that misuse of the evidence: see e.g., R. v. Corbett,  1 S.C.R. 670, at p. 691. The risk of misuse of evidence is particularly high in cases like this one where the Crown alleges morally reprehensible conduct in the context of the long-term abuse of one or more children within a household. When a jury hears the kind of evidence this jury heard, the trial judge must make it clear that the jury cannot use the evidence to infer that the accused is a bad person worthy of punishment regardless of his or her culpability on the specific allegations. The trial judge must also tell the jury that it cannot infer from that evidence that because the accused is the kind of person likely to abuse children, he or she is therefore guilty of the specific allegations.
The jurisprudence requiring a proper limiting instruction is loud and clear. For example, in R. v. B. (F.F.),  1 S.C.R. 697, the charges alleged that the accused had assaulted his niece over a number of years. Other children in the family came forward to give evidence of the physical abuse and brutality within the home. After explaining that the evidence of the accused's mistreatment of the other children was admissible to show the condition and atmosphere within the home and to explain the absence of any complaints, the court held that the trial judge should have given a proper limiting instruction. Iacobucci J. for the majority held at p. 734:
Given that the testimony might have a strong prejudicial effect on the jury and that the jury might then convict on the basis that the accused is a bad person of the sort likely to commit the offences in question, clear directions to the jury about the use they could make of the testimony were essential.More specifically, the judge was required to explain clearly in the instructions to the jurors that they must not infer from the evidence that tended to show the appellant's bad character that the appellant was guilty because he is the sort of person who is likely to commit the offences in question. [Emphasis added.]
This court has repeatedly applied the ratio from B. (F.F.) in cases like this one when properly admitted evidence inevitably blackened the character of the accused: see e.g. R. v. M. (B.) (1998), 42 O.R. (3d) 1 (C.A.), at pp. 9-10, 14; R. v. J.A.T., 2012 ONCA 177, 290 O.A.C. 130, at paras. 55, 67.