ClamAV
But on a serious note, no, I have no idea why that would happen.
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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
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ClamAV
But on a serious note, no, I have no idea why that would happen.
Was anything else installed on the 21st? Might have been pulled down as a dependency of something.
to answer this question: if you're on a dpkg-based system, check /var/log/dpkg.log
(or /var/log/dpkg.log.2.gz
to get logs from January, if your system rotates them once a month).
Or as a way for someone putting malware on the system to keep other malware away...
As a start, you can use opensnitch to see what connections it makes.
Or Wireshark