We have learned that one violates the prohibitions of bal yera’eh and bal yimatzei only by possessing ḥametz that is the property of a Jew, as it is written, “no ḥametz of yours shall be seen” (Shemot 13:7). Yet, at first glance, there is a difficulty here, for it is written, “there shall be no se’or found in your homes” (ibid. 12:19), implying that it is forbidden to have ḥametz in a Jewish home under any circumstances. The Sages explained that, indeed, if the ḥametz belongs to a gentile, and the Jew has not undertaken the responsibility of its safekeeping and guaranteeing its return, then it is not forbidden to have it in the Jew’s domain, as it is written, “and no ḥametz of yours shall be seen.” If, however, the Jew accepted responsibility for the item, then it is considered like his own, and the prohibition applies. This is what the Torah intended when commanding: “there shall be no se’or found in your homes” (Pesaḥim 5b).
Therefore, if a Jew guaranteed the return of ḥametz that was deposited with him, it becomes like his, and he is not allowed to keep it in his home or courtyard but must return it to the gentile or clear it out. Be-di’avad, if he cannot return it to the gentile and clearing it out will cause him a loss, he should sell the ḥametz together with the place it is stored, to a different gentile (SA 440:1; MB ad loc. 4). However, if the Jew undertook the protection of a gentile’s ḥametz that remains in the gentile’s possession, then the Jew does not violate any prohibition (MB 440:7). Thus, a Jewish-owned insurance company may insure a gentile’s ḥametz, because it remains in the gentile’s possession.
If a Jew deposited ḥametz with a fellow Jew for safekeeping, they are both obligated to eliminate it: the depositor because he owns it, and the custodian because, by committing to safeguard, it is considered his (SA 440:4). Even if he did not undertake its safekeeping, he is obligated to eliminate it.
If one bought stock in a company that owns ḥametz, and Pesaḥ arrived, if he has the authority to express his view about how to manage the company’s affairs – what to sell and what to buy – then it is considered as if he owns the ḥametz, and he violates bal yera’eh and bal yimatzei on account of it. But if he is not authorized to express an opinion, then he is like everyone who invests in stocks – the company owes him a percentage of its value, but its property is not considered his, and he does not violate any prohibitions on account of its ḥametz holdings. Accordingly, those who invest money in mutual funds or pension funds do not violate any ḥametz prohibitions, even though the managers of the funds may invest part of the money in a company that owns ḥametz, since this ḥametz is not considered the property of the investor. Some rule stringently in this case.
. Regarding a Jew who deposited his ḥametz with another person, SA 440:4 rules in accordance with R. Yona that even if the custodian accepts responsibility over the ḥametz, since the ḥametz still belongs to the owner, it is the owner’s responsibility to destroy it. This is the opinion of other poskim as well. According to Ramban and Ran, since the ḥametz is not in the owner’s possession and the custodian accepted responsibility for it, the owner of the ḥametz does not transgress any prohibition. As for the custodian, SA 443:2 states that if the owner of the ḥametz did not come to collect it before Pesaḥ, the custodian should preferably sell the ḥametz to a gentile in order to preserve its value. If he did not do so, the custodian is obligated to destroy the ḥametz. MB ad loc. (14) explains that according to Baḥ and MA, the reason for this obligation is that every Jew is responsible for his fellow Jew (“kol Yisrael areivim zeh la-zeh”). Gra’s opinion on the matter is that even if the custodian did not accept responsibility for the ḥametz, he still has a Torah obligation to destroy it, as it is forbidden to harbor a Jew’s ḥametz in one’s home. This is also the opinion of Tzlaḥ and Beit Meir.
. So states She’arim Metzuyanim Be-halakha 114:28. Some are strict and sell their shares of ḥametz-owning companies and companies that insure ḥametz. So states Sidur Pesaḥ Ke-hilkhato 11:5. Many ḥametz-sale documents include provisions to address this (see Piskei Teshuvot 440:1).