OJS, like any free and open-source software (FOSS), is built by a community of developers using publicly available source code. Unfortunately this open availability also gives access to hackers and malicious users.
Google Scholar, one of the largest A&I services in existence, indexes almost any journal and likely accounts for more than half of all referrals to online journals. Google Scholar is also very important as its large open index of scholarly articles is easily accessible for most readers. It also does an excellent job of finding multiple versions of scholarly articles and theses.