I’d add that it was an unencrypted public Wi-Fi network which, in hindsight, could’ve been spoofed. (Yes, very careless of me…) Windows XP’s built-in firewall was also found to be off after the Wi-Fi session.

ran Avast (including a boot-time scan with high heuristics) and two other anti-virus/trojan programs, but there was no sign of any infection.

I used Malwarebytes Anti-Malware and a2 Emergency Kit to scan the computer manually and sequentially. I only have one anti-virus program (Avast) on at any given time.