I rarely enter my wallet, what i do is check the balance on blockchain explorer to see if the btc is still there. This morning when i checked my  btc address, i saw that my balance of 0.3 btc had reduced to 0.0006 btc. When i saw that i had small heart attack and quickly entered my Electrum wallet. Thankfully my money was still there but had been transferred to a new address. I'm certain i have never done any transfers on that wallet. How did it happen? Is that a glitch or should i be worried?

Thank you