There was a report at ars Technica that the journal Tumor Biology is retracting staggering 107 research papers due to fraudulent peer review process. It appears that such practice has been an on-going business. According to the report, last year 58 papers were retracted from 7 different journals (the report does not specify what they are but I suspect mostly biology journals) and 25 of them came from Tumor Biology. What happened was that when authors submitted their manuscripts for review the editorial office asked the authors to recommend reviewers (the editors perhaps assumed that the authors would suggest best possible reviewers with no conflict of interest who would give a fair and professional review). Apparently the process was abused by some authors and they recommended people they know personally who would give their papers a favorable review regardless of their academic value. I would say those journals are also responsible for the mayhem as they basically let it happen. If people think that scientists would always conduct their research and academic activities with honesty, pride and integrity, they would be flatly naive and wrong. Research publication is directly tied to tenure, promotion and also grants (especially in biological sciences grants come with a big money). Never think that academia would never spoil. Scientists are also men with many flaws. Unfortunately for some often these things weigh more than their pride and academic integrity.
Theoretical physics journals have the same kind of review process but there is little room for such fraudulent practice as it is relatively easier for any third party experts to verify the results and academic merits of a paper in theoretical physics. While theoretical physics research often comes with hypes of all levels, it is relatively much more honest area compared with certain experimental sciences. Without any bias, mathematics is certainly the most honest area. If you are not honest about what you do, you really cannot be a good mathematician. Also there is no room for cooking up your results as everything is readily verifiable by experts. In mathematics, most common malpractices are abusing citation and plagiarism. But such malpractices have never been a big issue in mathematics community as no serious mathematicians would even think of committing them. Whoever commit such things could/would never be regarded as a mathematician.