There's only one way to test if you've been infected.
Get a random address from your wallet, paste it to the send tab/text file; if the pasted address is different, then it's the culprit.
If it's your friend, tell him to check the address he sent to you (not in the wallet but in the message) if it matched to any of his wallet's addresses.

Note: Check all the characters, the common malware can generate similar addresses with same first and last few characters.