Disclosure upfront: we make Shiny, a $4.99 menu-bar app that frees memory. MacBooster covers memory among several other jobs, which makes us a competitor for that one feature. We've tried to write this the way we'd want it written as a buyer.
The honest verdict
MacBooster is developed by IObit, a Chinese software company that has been making Windows and Mac utilities since 2004, also known for Advanced SystemCare and IObit Uninstaller. MacBooster is a signed, notarized macOS application, meaning it has passed Apple's security screening and will not silently install malware on your Mac.
That said, "not malware" and "trusted by the security community" are different things. Malwarebytes, a well-regarded anti-malware vendor, flags MacBooster as a potentially unwanted program (PUP), a category reserved for software that is not outright malicious but uses tactics security researchers consider aggressive or manipulative, typically inflated scan results or high-pressure upsells. Macworld's own review of MacBooster states plainly that "it's no surprise people think it's malware," a striking line for a mainstream tech publication to publish about a paid product.
Why the reputation problem exists
The pattern security researchers point to is common across the "system optimizer" category MacBooster belongs to: a free or trial scan reports a large number of "issues" (often duplicated across categories, or issues that pose no real risk), creating pressure to purchase the paid version to "fix" them. This is the same mechanism that earned MacKeeper its scareware reputation in the 2010s, though MacBooster's current marketing is less aggressive than MacKeeper's historical peak.
Reddit threads discussing MacBooster skew negative, with users reporting inflated problem counts and describing the upsell pressure as uncomfortable. This is consistent with the Malwarebytes PUP classification rather than contradicting it.
What MacBooster actually does
Stripped of the marketing, MacBooster's real feature set covers: junk file and cache cleanup, a memory optimizer that frees inactive RAM, a "Turbo Boost" one-click performance mode, an app uninstaller, a privacy cleaner that removes browser history and cookies, and disk space optimization. None of these jobs are inherently suspect; they are the same jobs CleanMyMac, MacKeeper, and other suites perform. The concern is specifically about how aggressively the scan results are presented and how hard the upsell is, not about the underlying functionality being dangerous.
Pricing is subscription-only, ranging from roughly $39.95 to $89.95 per year depending on the number of Macs covered. There is no one-time purchase option.
Should you use it?
MacBooster might suit you if you've read the concerns above, understand the upsell tactics to expect, and still want the specific bundle of features at the subscription price.
MacBooster probably doesn't suit you if the PUP classification and negative Reddit sentiment give you pause (reasonable), you only want one of its jobs rather than the bundle, or you prefer to avoid subscription pricing.
For the memory job specifically, there are cheaper and more narrowly scoped alternatives with cleaner reputations: Shiny ($4.99 once) or Memory Cleaner (free with paid extras) do that one job without the bundled upsell pressure. For a full suite with a notably cleaner track record, CleanMyMac is the more established, better-reviewed option in the same broad category.
What "potentially unwanted program" actually means
It's worth being precise about the PUP classification rather than treating it as a vague red flag. Security vendors use the PUP label for software that does what it says (in MacBooster's case, genuine cleanup and optimisation functions) but ships with behaviour the vendor considers manipulative: commonly, scan results inflated to make a Mac look more "at risk" than it actually is, or checkout flows designed to make declining the upgrade harder to find than accepting it. That's a real, documented pattern, but it's a different and less severe concern than a virus or trojan, which is why "not malware" and "flagged as a PUP" can both be true statements about the same app at the same time.
The honest comparison to MacKeeper's history
It's worth noting the parallel: MacKeeper spent a decade rebuilding its reputation after a genuinely aggressive scareware era, and largely succeeded, with a cleaner current product under new ownership. MacBooster has not gone through that same public reckoning; the PUP flag and the Macworld quote suggest similar concerns are current, not historical. That's a meaningful difference when deciding how much trust to extend.
What to do if you've already installed it
If MacBooster is already on your Mac and you want to move on, uninstalling it cleanly is straightforward: open the app, look for its own uninstall option in the menu bar or preferences, and follow the prompts. If you want to be thorough about leftover files afterward, a free tool like AppCleaner can scan for any preference files, caches, or support folders the built-in uninstaller missed. None of this requires urgency in a security sense (MacBooster is not malware and won't actively harm your Mac while you decide), but if the concerns in this post have changed your mind, removing it is a simple, low-stakes process.