Mine was GIANT-AntiSpyware
It looks like some rogue Antivirus but it was one of the better GUI's in those days
Giant AntiSpyware was owned by two guys that had a partnership, one sold his half to Microsoft which first became Windows Defender then Microsoft Security Essentials. The same engine is still used today on Windows 8 Windows Defender of coarse it is updated.
The other guy sold his half to Sunbelt which became CounterSpy then VIPRE, it is still the same engine but also updated.
After the deal was done both Microsoft and Sunbelt shared the same exact database for a year before going their separate ways.
My first AV was eTrust Antivirus on Windows 95 long before CA bought them out. Then I used Norton, McAfee and TrendMicro, back in those days you didn't have much options. There were no free AV's available back then. Around 2000 Nod32 came out and I stayed with it for awhile because it didn't slow down my systems like the others did and it was cheaper.