Target-rich environment: Why Microsoft 365 has become the biggest risk

Microsoft 365 has become the central nervous system of modern business — and cybercriminals know it. Just as Windows became the primary target for attackers because of its market dominance in the 1990s and 2000s, Microsoft 365 now finds itself in the crosshairs for having "won" the email and collaboration war. With over 400 million paid Office 365 seats worldwide and countless organizations relying on its integrated suite of applications, Microsoft 365 represents the ultimate target-rich environment for threat actors. The winner's curse: Success breeds risk The parallel between Windows' security journey and Microsoft 365's current predicament is striking. Windows has become a prime target of attacks across the operating systems market not because it was inherently less secure than alternatives, but because attacking Windows meant accessing the largest possible pool of potential victims. Today, Microsoft 365 faces the same winner's curse. Having successfully consolidated email, file sharing, collaboration and communication into a single ecosystem, Microsoft 365 has painted a massive target on its back. This dominance creates a multiplication effect for attackers. A single successful campaign targeting Microsoft 365 can potentially impact millions of users across thousands of organizations. For cybercriminals operating on a cost-benefit analysis, the math is simple: Why develop separate attack vectors for multiple platforms when you can focus your efforts on the one platform that reaches the most targets? Multisurface threat vectors Microsoft 365 presents a complex web of interconnected services that dramatically expand the attack surface. Each application — Outlook, SharePoint, Teams and OneDrive — represents a potential entry point, and their tight integration means compromising one service provides pathways to others. This creates "lateral movement opportunities." An attacker gaining access through phishing in Outlook can pivot to exfiltrate SharePoint data, manipulate OneDrive documents or join confidential Teams meetings. The seamless experience that appeals to businesses becomes a dream scenario for attackers seeking to maximize impact. Recent SharePoint vulnerabilities highlight this danger. In July 2025, Microsoft patched zero-day vulnerabilities including CVE-2025-53770, that was actively exploited against on-premises SharePoint customers since July 7, affecting over 75 servers. These attacks demonstrate cascading risk, where compromising SharePoint provides access to the entire collaborative infrastructure. All-in-one integrated backup and cybersecurity platform for MSPs Acronis Cyber Protect Cloud integrates data protection, cybersecurity, and endpoint management. Easily scale cyber protection services from a single platform – while efficiently running your MSP business. Free 30-day Trial Hidden in plain sight: The backup blind spot One of the most overlooked risks in Microsoft 365 environments lies in backup and recovery systems. Many organizations assume that Microsoft's built-in retention policies and version history provide adequate protection, but this creates dangerous blind spots. Standard Microsoft 365 backups often lack the granular recovery options needed to respond to sophisticated attacks, and worse, they can actually store and preserve malicious content that becomes a future attack vector. When scanning URLs in Microsoft 365 email backups, analysts discovered that 40% contained phishing links that had been dutifully preserved alongside legitimate business communications. Even more alarming, over 200,000 backed-up emails contained malware attachments. These findings expose a critical flaw in traditional backup approaches: Organizations are not just storing their data — they're creating permanent archives of the very threats designed to destroy them. This means that restoring from backup after a security incident could potentially reintroduce the original attack vectors back into the environment. When ransomware actors encrypt SharePoint libraries or corrupt Exchange mailboxes, having robust, isolated backups becomes the difference between a quick recovery and a business-ending catastrophe. Yet many MSPs and IT teams discover too late that their backup strategies have critical gaps when facing modern threats that specifically target cloud collaboration platforms. Hardening without hampering MSPs and IT teams must implement robust security controls without undermining Microsoft 365's productivity benefits. This requires layered defenses beyond native security features. Zero trust architecture becomes essential, with continuous verification of user identities and device health. Multifactor authentication should be non-negotiable but implemented to avoid user friction that drives workarounds. Advanced threat protection must extend across all Microsoft 365 applications — from SharePoint document scanning to Teams monitoring and OneDrive behavior analysis. Security teams need cross-application visibility to detect anomalous access patterns. Regular assessments should focus on Microsoft 365 configurations, including Power Platform permissions, third-party integrations and guest access controls. The ecosystem's complexity means misconfigurations can create persistent security gaps. The path forward Microsoft 365's dominance makes it an inevitable target. Organizations must recognize that securing it requires specialized expertise and tools tailored to cloud collaboration threats. The goal isn't to abandon Microsoft 365 — its benefits are too significant. Instead, organizations must acknowledge elevated risks and implement proportionate measures, treating Microsoft 365 security as a specialized discipline, not a checkbox item. Organizations that proactively harden defenses maintain a competitive advantage while protecting sensitive assets. Those that don't learn the hard way why being the biggest target brings the biggest risks. About TRU The Acronis Threat Research Unit (TRU) is a team of cybersecurity experts specializing in threat intelligence, AI and risk management. The TRU team researches emerging threats, provides security insights, and supports IT teams with guidelines, incident response and educational workshops. See the latest TRU research. Sponsored and written by Acronis.