Users that run unpatched software beware. Hackers have been relying on an old software bug tied to the Stuxnet worm to carry out their attacks.
Microsoft may have initially patched the flaw in 2010, but it's nevertheless become the most widespread software exploit, according to security firm Kaspersky Lab.
On Thursday, Kaspersky posted research examining the use of exploits, or malicious programs designed to take advantage of certain software flaws. Once an exploit goes to work, it can typically pave the way for other malicious programs to install onto a computer.
In 2015, and in 2016, it was used to target about a quarter of Kaspersky users who had encountered an exploit, the security firm said.
Fortunately, the vulnerability only affects older systems such as Windows XP, Windows Server 2008, and Windows 7. But that hasn't stopped hackers from finding susceptible systems.
The hackers behind these exploits have been using them in malware that can "self-replicate" over a network and remain on affected computers, Kaspersky said.
The lesson: Hackers can still succeed when computers are still running out-of-date software. The research from Kaspersky highlights other well-known vulnerabilities in Microsoft Office, Android, and Java that hackers are still targeting, despite past software fixes.
"The life of an exploit doesn’t end with the release of a security patch," the security firm said.
The warning isn’t new. But lately, the security community has been stressing the need for users and businesses to keep their software up to date. Last week, a mysterious group released a cache of suspected U.S. government spying tools that anyone can now use to hack older Windows systems.
Microsoft has already issued patches fixing the software flaws the tools target. However, an older operating system like Windows Server 2003 will remain vulnerable indefinitely to some of the risks because Microsoft no longer supports the software.
"Any remaining Windows Server 2003 machines should be upgraded immediately," security provider Rendition InfoSec said in a blog post.