NEW YORK, ( TheStreet) - Hewlett-Packard ( HPQ) continued its acquisition spree with a $1.5 billion proposed buyout of network security shop ArcSight ( ARST) Monday. Just 11 days after HP won a bidding war against Dell ( DELL) for storage specialist 3Par ( PAR) for $2.06 billion, the computer giant makes another deal to further expand its business beyond PCs. ArcSight shares had been trading at 52-week highs this month as merger speculation heated interest in the company, which recently put itself on the sales block. HP says it will pay $43.50 in cash for all of the outstanding shares of ArcSight and expects the deal to close by year-end. ArcSight shares jumped $8.58, or 24%, To $43.68 in premarket trading Monday. --Written by Scott Moritz in New York.>To contact this writer, click here: Scott Moritz, or email: email@example.com.To follow Scott on Twitter, go to http://twitter.com/TheStreet_Tech.>To send a tip, email: firstname.lastname@example.org.