Check out which companies are making headlines after Monday's close:
Sonic - The drive-in restaurant chain posted first-quarter earnings of 13 cents a share on revenues of $126.7 million. Analysts had estimated earnings per share of 13 cents on revenue of $128 million. Shares rallied 4.6 percent in after-hours trading.
Palo Alto Networks - The network-security platform provider rallied in extended-hours trade after it said it acquired Morta Security, a cybersecurity company. Financial terms were not disclosed.
—By CNBC's Kate Gibson.
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