Symantec Corp.  (SYMC - Get Report) shares plunged Monday amid reports that chipmaker Broadcom (AVGO - Get Report) has walked away from takeover talks with the cybersecurity firm.

CNBC reported that Broadcom was unwilling to extend any offer past $28 a share, a level that Symantec had insisted upon in order to give a fair valuation to its overall business, which includes its Norton and LifeLock product suites. The pair were said to be in 'advanced' talks earlier this month that analysts had assumed would lead to a deal that valued Symantec in the region of $15 billion to $20 billion.

Symantec shares were marked 13.6% lower at the start of trading Monday to change hands at $22.12 each, the lowest since late June and a level that would give the Mountain View, California-based antivirus software firm a market value of around $13.5 billion. Broadcom shares, meanwhile, were seen 3.1% higher at $294.26 each.

Broadcom CEO Hock Tan told investors last month, after his company's second quarter earnings that "businesses that are franchises that we see as very sustainable and that we are able to acquire" would likely be Broadcom's near-term takeover targets, noting "we continue to be very interested in opportunities that may present themselves and we continue to be very active in assessing those opportunities."

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