Texas-based Dell did not disclose financial terms of the acquisition, which was estimated in online reports to tally more than a billion dollars.
"Our customers see security as a key IT concern for the foreseeable future," Dell software group president John Swainson said in a release.
"We are building a strategic software portfolio to address the needs of our customers with key assets in the fast-growing and highly profitable IT security solutions business," he added.
SonicWALL was founded in 1991 and has its headquarters in the Silicon Valley city of San Jose.
More than 300,000 customers spread about 50 countries use SonicWALL products such as computer firewalls, email defenses, and software for secure remote access to networks, according to Dell.
"Dell's phenomenal breadth and reach into small and mid-size companies provides a significant opportunity to expand our customer base," said SonicWALL chief executive Matt Medeiros.