plugins problems

hallo:)
I have just started up my own website, and until now, I have only installed plugins (Antivirus,BPS,Exploit scanner,secure wordpress, TAC and WP-malwatch) to secure my site.when I scan with exploit scanner it shows me 16 level severes? ex. located from plugin: antivirus and wp-malwatch an secure wordpress. in this it shows base64 and eval.. how can that be possible? Are these plugins not secure to use?
Hope someone can help me:)